Summary and roadmap
\[\gdef\badDispatch#1{\textbf{\textcolor{e1432d}{#1}}} \gdef\noKatexForm#1{\badDispatch{#1}} \gdef\largeDot{\raisebox{0.06em}{\tiny∙}} \gdef\rarrbar{{\raisebox{-0.05em}{→}\mkern{-0.13em}{\large\shortmid}}} \gdef\larrbar{{{\large\shortmid}\mkern{-0.13em}{\raisebox{-0.05em}{←}}}} \gdef\suptrans{^\mathsf{T}} \gdef\supdagger{^\dagger} \gdef\cardinalRewrite#1#2{\rewrite{#1}{#2}} \gdef\primed#1{{#1}^{\prime}} \gdef\tinybullet{{\tiny●}} \gdef\factsym#1{\mathord{#1}} \gdef\forwardFactor{\factsym{\uparrow}} \gdef\backwardFactor{\factsym{\downarrow}} \gdef\forwardBackwardFactor{\factsym{\updownarrow}} \gdef\forwardBackwardNeutralFactor{\factsym{\mathrlap{\downarrow}{\mathrlap{\uparrow}{\endash} } }} \gdef\neutralFactor{\factsym{\shornarrow}} \gdef\edgedot{↫} \gdef\desym{\mathbin{↣}} \gdef\uesym{\mathbin{↢}} \gdef\de#1#2{{{#1}\desym{#2}}} \gdef\ue#1#2{{{#1}\uesym{#2}}} \gdef\shifttag#1{\raisebox{-1em}{$#1$}} \gdef\shifttag#1{#1} \gdef\tde#1#2#3{{#1}\:\xrightedge{\shifttag{#3}}\;{#2}} \gdef\tue#1#2#3{{#1}\;\xundirectededge{\shifttag{#3}}\;{#2}} \gdef\shiftunderset#1#2{\underset{\raisebox{0.15em}{\scriptsize $#1$}}{#2}} \gdef\mdtde#1#2#3#4{{#1}\,\;\shiftunderset{#4}{\xrightedge{#3}}\;{#2}} \gdef\mtue#1#2#3#4{{#1}\,\;\shiftunderset{#4}{\xundirectededge{#3}}\;\,{#2}} \gdef\mtde#1#2#3#4{{#1}\,\;\operatornamewithlimits{\xrightedge{#3}}\limits_{#4} \;{#2}} \gdef\mapsfrom{\htmlClass{hreflect}{\mapsto}} \gdef\longmapsfrom{\htmlClass{hreflect}{\longmapsto}} \gdef\diffd{𝕕} \gdef\partialdof#1{\partial {#1}} \gdef\textAnd{\text{\,and\,}} \gdef\identicallyEqualSymbol{\equiv} \gdef\congruentSymbol{\equiv} \gdef\isomorphicSymbol{\simeq} \gdef\homeomorphicSymbol{\cong} \gdef\homotopicSymbol{\simeq} \gdef\approxEqualSymbol{\approx} \gdef\bijectiveSymbol{\approx} \gdef\defeq{\mathrel{≝}} \gdef\defEqualSymbol{\mathrel{≝}} \gdef\syntaxEqualSymbol{\mathrel{\textcolor{888888}{\equiv}}} \gdef\tailEqualSymbol{\underdot{=}} \gdef\headEqualSymbol{\dot{=}} \gdef\ruledelayed{:\to} \gdef\mathdollar{\text{\textdollar}} \gdef\hyphen{\text{-}} \gdef\endash{\text{--}} \gdef\emdash{\text{---}} \gdef\updownarrows{\uparrow\!\downarrow} \gdef\vthinspace{\mkern{1pt}} \gdef\dlq{\text{\textquotedblleft}} \gdef\drq{\text{\textquotedblright}} \gdef\dprime{{\prime\prime}} \gdef\inverse#1{{{#1}^{-1}}} \gdef\inverseSymbol{\inverse{□}} \gdef\groupDirectProduct#1{#1} \gdef\groupDirectProductSymbol{\times} \gdef\groupInverse{\inverse} \gdef\groupPower#1#2{{#1}^{#2}} \gdef\groupCommutator#1#2{\left[{#1},{#2}\right]} \gdef\groupoidInverse{\inverse} \gdef\latticeBFS#1{\textrm{bfs}({#1})} \gdef\pathHomomorphism#1{#1} \gdef\groupoidFunction#1{#1} \gdef\groupoidHomomorphism#1{#1} \gdef\affineModifier#1{\overrightharpoon{#1}} \gdef\supercirc#1{#1^{\circ}} \gdef\supercircb#1{#1^{\bullet}} \gdef\blackCircleModifier#1{\supercircb{#1}} \gdef\whiteCircleModifier#1{\supercirc{#1}} \gdef\totalSpaceStyle#1{\piFo{#1}} \gdef\baseSpaceStyle#1{\blFo{#1}} \gdef\fiberSpaceStyle#1{\reFo{#1}} \gdef\totalSpaceElementStyle#1{\daPiFo{#1}} \gdef\baseSpaceElementStyle#1{\daBlFo{#1}} \gdef\fiberSpaceElementStyle#1{\daReFo{#1}} \gdef\bundleProjectionStyle#1{\daGrFo{#1}} \gdef\bundleGraphStyle#1{\piFo{#1}} \gdef\bundleSectionStyle#1{\daOrFo{#1}} \gdef\bundleFunctionStyle#1{\daPiFo{#1}} \gdef\graphFunctionStyle#1{\totalSpaceStyle{#1}} \gdef\projectionFunctionStyle#1{\totalSpaceStyle{#1}} \gdef\sectionFunctionStyle#1{\totalSpaceStyle{#1}} \gdef\functionGraph#1{G_{#1}} \gdef\toroidalModifier#1{\supercirc{#1}} \gdef\modulo#1{\supercirc{#1}} \gdef\dividesSymbol{\mathrel{|}} \gdef\groupFunction#1{#1} \gdef\groupHomomorphism#1{#1} \gdef\automorphisms{\operatorname{Aut}} \gdef\endomorphisms{\operatorname{End}} \gdef\transportMap#1{\transportMapSymbol_{#1}} \gdef\transportMapSymbol{\tau} \gdef\action#1{#1} \gdef\selfAction#1{\hat{#1}} \gdef\actionGroupoid#1{\utilde{#1}} \gdef\cardinalGroup#1{G^*({#1})} \gdef\signed#1{{#1}^*} \gdef\transportAtlas#1{T_{#1}} \gdef\inverted#1{\underline{#1}} \gdef\mirror#1{\overline{#1}} \gdef\pathComposeSymbol{\mathbin{∷}} \gdef\pathCompose#1#2{{#1}\pathComposeSymbol{#2}} \gdef\translateSymbol{\mathbin{\uparrow}} \gdef\backwardTranslateSymbol{\mathbin{\downarrow}} \gdef\pathHead#1{\pathHeadVector{#1}} \gdef\pathTail#1{\pathTailVector{#1}} \gdef\pathHeadVector#1{{#1}^{\bullet}} \gdef\pathTailVector#1{{#1}_{\bullet}} \gdef\pathReverse#1{{#1}^{\dagger}} \gdef\pathIntegral#1#2{{#1} \int {#2}} \gdef\pathIntegralSymbol{{\int}} \gdef\pathDot#1#2{{#1} \cdot {#2}} \gdef\pathDotSymbol{{\cdot}} \gdef\compactBasis#1{\mathscr{B}} \gdef\length{\operatorname{len}} \gdef\signedLength{\operatorname{len^*}} \gdef\andFn{\operatorname{and}} \gdef\orFn{\operatorname{or}} \gdef\notFn{\operatorname{not}} \gdef\vertexList{\operatorname{vertices}} \gdef\vertexList{\operatorname{vertices}} \gdef\edgeList{\operatorname{edges}} \gdef\pathList{\operatorname{paths}} \gdef\cardinalList{\operatorname{cards}} \gdef\signedCardinalList{\operatorname{cards^*}} \gdef\wordOf{\operatorname{word}} \gdef\headVertex{\operatorname{head}} \gdef\tailVertex{\operatorname{tail}} \gdef\basis{\operatorname{basis}} \gdef\split{\operatorname{split}} \gdef\lcm{\operatorname{lcm}} \gdef\minimalContractionSets{\operatorname{MCSets}} \gdef\minimalContractions{\operatorname{MC}} \gdef\grade{\operatorname{grade}} \gdef\support{\operatorname{support}} \gdef\coefficient{\operatorname{coeff}} \gdef\domain{\operatorname{domain}} \gdef\codomain{\operatorname{codomain}} \gdef\modFunction{\operatorname{mod}} \gdef\clip{\operatorname{clip}} \gdef\sign{\operatorname{sign}} \gdef\step{\operatorname{step}} \gdef\projection{\operatorname{proj}} \gdef\lift{\operatorname{lift}} \gdef\identity{\operatorname{id}} \gdef\total{\operatorname{total}} \gdef\torus{\operatorname{torus}} \gdef\mobius{\operatorname{mobius}} \gdef\stateCompose{\operatorname{glue}} \gdef\infixStateComposeSymbol{\_} \gdef\stateDecompose{\operatorname{melt}} \gdef\stateJoin{\operatorname{conj}} \gdef\stateMeet{\operatorname{disj}} \gdef\stateExtent{\operatorname{extent}} \gdef\stateIntent{\operatorname{intent}} \gdef\infixStateJoinSymbol{\sqcup} \gdef\infixStateMeetSymbol{\sqcap} \gdef\isPrime#1{#1\textrm{ prime}} \gdef\blank{\_} \gdef\emptyWord{} \gdef\multiwordSymbol#1{\mathbf{#1}} \gdef\wordSymbol#1{\mathtt{#1}} \gdef\word#1{#1} \gdef\pathMap#1{#1} \gdef\function#1{#1} \gdef\imageModifier#1{{#1}^{\rightarrow}} \gdef\preimageModifier#1{{#1}^{\leftarrow}} \gdef\multiImageColorModifier#1{\msetCol{#1}} \gdef\multiImageModifier#1{{#1}^{\Rightarrow}} \gdef\multiPreimageModifier#1{{#1}^{\Leftarrow}} \gdef\functionComposition#1{#1} \gdef\functionCompositionSymbol{\mathbin{\small ∘}} \gdef\rightFunctionComposition#1{#1} \gdef\rightFunctionCompositionSymbol{\mathbin{\tiny ●}} \gdef\route#1#2#3{[{#1}\!:\!{#2}\!:\!{#3}]} \gdef\multiroute#1#2#3{[{#1}\!:\!{#2}\!:\!{#3}]} \gdef\pathWord#1#2#3{{#1}\!:\!{#2}\!:\!{#3}} \gdef\parenPathWord#1#2#3{\left(\pathWord{#1}{#2}{#3}\right)} \gdef\nullPath{\bot} \gdef\nullElement{\bot} \gdef\path#1{#1} \gdef\vert#1{#1} \gdef\underdot#1{\underset{\raisebox{0.3em}{.}}{#1}} \gdef\headVertexSymbol{◨} \gdef\tailVertexSymbol{◧} \gdef\placeholderVertexSymbol{\mathrlap{◨}{◧}} \gdef\tvert#1{\underdot{#1}} \gdef\hvert#1{\dot{#1}} \gdef\edge#1{#1} \gdef\card#1{\mathtt{#1}} \gdef\path#1{#1} \gdef\quiver#1{#1} \gdef\bindingRuleSymbol{\to} \gdef\compactBindingRuleSymbol{:} \gdef\cayleyQuiverSymbol#1{\selfAction{#1}} \gdef\bindCayleyQuiver#1#2{\selfAction{#1}[#2]} \gdef\bindActionQuiver#1#2{#1[#2]} \gdef\bindSize#1#2{#1(#2)} \gdef\bindCardSize#1#2{#1[#2]} \gdef\bindCards#1#2{#1[#2]} \gdef\subSize#1#2{#1_{#2}} \gdef\gridQuiver#1{\textrm{Grid}^{#1}} \gdef\treeQuiver#1{\textrm{Tree}^{#1}} \gdef\bouquetQuiver#1{\textrm{Bq}^{#1}} \gdef\lineQuiver{\textrm{L}} \gdef\cycleQuiver{\textrm{C}} \gdef\squareQuiver{\textrm{Sq}} \gdef\cubicQuiver{\textrm{Cbc}} \gdef\triangularQuiver{\textrm{Tri}} \gdef\hexagonalQuiver{\textrm{Hex}} \gdef\rhombilleQuiver{\textrm{Rmb}} \gdef\limit#1#2{\lim_{#2}\,#1} \gdef\realVectorSpace#1{\mathbb{R}^{#1}} \gdef\complexVectorSpace#1{\mathbb{C}^{#1}} \gdef\matrixRing#1#2{M_{#2}(#1)} \gdef\groupoid#1{#1} \gdef\group#1{#1} \gdef\field#1{#1} \gdef\ring#1{#1} \gdef\variable#1{#1} \gdef\semiring#1{#1} \gdef\sym#1{#1} \gdef\matrix#1{#1} \gdef\tupleSym#1{#1} \gdef\polynomial#1{#1} \gdef\setLetter{\mathcal{S}} \gdef\signedSetLetter{\mathcal{S^*}} \gdef\multisetLetter{\mathcal{M}} \gdef\signedMultisetLetter{\mathcal{M^*}} \gdef\multisetSemiringSymbol#1{#1} \gdef\multisetSemiring#1#2{\multisetLetter\left[#1, #2\right]} \gdef\signedMultisetRingSymbol#1{#1} \gdef\signedMultisetRing#1#2{\signedMultisetLetter\left[#1, #2\right]} \gdef\polynomialRing#1#2{#1[{#2}]} \gdef\routeSymbol#1{#1} \gdef\multirouteSymbol#1{\mathbf{#1}} \gdef\planSymbol#1{\mathbf{#1}} \gdef\ringElement#1{#1} \gdef\tuplePart#1#2{#1\llbracket{#2}\rrbracket} \gdef\matrixPart#1#2#3{#1\llbracket{#2,#3}\rrbracket} \gdef\matrixRowPart#1{#1} \gdef\matrixColumnPart#1{#1} \gdef\subMatrixPart#1#2#3{#1_{#2,#3}} \gdef\matrixDotSymbol{\cdot} \gdef\matrixPlusSymbol{+} \gdef\wordGroup#1{\wordGroupSymbol_{#1}} \gdef\wordGroupSymbol{\Omega} \gdef\wordRing#1{\wordRingSymbol_{#1}} \gdef\wordRingSymbol{\Omega\!\degree} \gdef\wordRingElement#1{#1} \gdef\wordRingBasisElement#1{e_{#1}} \gdef\linearCombinationCoefficient#1{{\textcolor{888888}{#1}}} \gdef\plan#1{#1} \gdef\planRing#1{\planRingSymbol_{#1}} \gdef\planRingSymbol{\Phi} \gdef\basisPath#1#2{\mathbf{#1}_{#2}} \gdef\basisPathWeight#1#2{{#1}_{#2}} \gdef\unitSymbol{\mathbf{e}} \gdef\unitVertexField{\unitSymbol_1} \gdef\forwardSymbol{f} \gdef\backwardSymbol{b} \gdef\symmetricSymbol{s} \gdef\antisymmetricSymbol{a} \gdef\wordVector#1#2{\unitSymbol_{#1}^{#2}} \gdef\gradOf#1{\grad\,{#1}} \gdef\grad{\nabla} \gdef\divOf#1{\div\,{#1}} \gdef\div{\dot{\nabla}} \gdef\laplacianOf#1{\laplacian\,{#1}} \gdef\laplacian{\ddot{\nabla}} \gdef\suchThat#1#2{{#1}\,\big|\,{#2}} \gdef\chart#1{\chartSymbol_{#1}} \gdef\chartSymbol{C} \gdef\graphRegionIntersectionSymbol{\cap} \gdef\graphRegionUnionSymbol{\cup} \gdef\pathIso{\simeq} \gdef\factorial#1{#1!} \gdef\power#1#2{{#1}^{#2}} \gdef\repeatedPower#1#2{{#1}^{#2}} \gdef\kroneckerDeltaForm#1{\kroneckerDeltaSymbol_{#1}} \gdef\kroneckerDeltaSymbol{\delta} \gdef\contractionLattice#1{\operatorname{Con}(#1)} \gdef\contractedRelation#1{\sim_{#1}} \gdef\isContracted#1#2{{#1} \sim {#2}} \gdef\isContractedIn#1#2#3{{#1} \sim_{#3} {#2}} \gdef\isNotContracted#1#2{{#1} \not \sim {#2}} \gdef\isNotContractedIn#1#2#3{{#1} \not \sim_{#3} {#2}} \gdef\contractionSum#1{#1} \gdef\contractionSumSymbol{\sqcup} \gdef\contractionProduct#1{#1} \gdef\contractionProductSymbol{{\cdot}} \gdef\graph#1{#1} \gdef\graphHomomorphism#1{#1} \gdef\coversSymbol{\sqsupseteq} \gdef\coveredBySymbol{\sqsubseteq} \gdef\strictlyCoversSymbol{\sqsupset} \gdef\strictlyCoveredBySymbol{\sqsubset} \gdef\graphCovering#1#2#3{{#2} \sqsupseteq_{#1} {#3}} \gdef\quiverCovering#1#2#3{{#2} \sqsupseteq^{#1} {#3}} \gdef\powerSetSymbol{\mathcal{P}} \gdef\powerSet#1{\powerSetSymbol({#1})} \gdef\existsForm#1#2{\exists\,{#1}\,:\,{#2}} \gdef\forAllForm#1#2{\forall\,{#1}\,:\,{#2}} \gdef\notted#1{\notSymbol {#1}} \gdef\andSymbol{\land} \gdef\orSymbol{\lor} \gdef\notSymbol{\lnot} \gdef\latticeSymbol#1{#1} \gdef\meetSemilatticeSymbol#1{#1} \gdef\joinSemilatticeSymbol#1{#1} \gdef\posetSymbol#1{#1} \gdef\latticeElementSymbol#1{#1} \gdef\meetSemilatticeElementSymbol#1{#1} \gdef\joinSemilatticeElementSymbol#1{#1} \gdef\posetElementSymbol#1{#1} \gdef\latticeMeetSymbol{\wedge} \gdef\latticeJoinSymbol{\vee} \gdef\latticeTop{\top} \gdef\latticeBottom{\bot} \gdef\semilatticeMeetSymbol{\wedge} \gdef\semilatticeJoinSymbol{\vee} \gdef\semilatticeTop{\top} \gdef\semilatticeBottom{\bot} \gdef\semilatticeSemimeetSymbol{\wedge} \gdef\semilatticeSemijoinSymbol{\vee} \gdef\latticeGreaterSymbol{>} \gdef\latticeGreaterEqualSymbol{\ge} \gdef\latticeLessSymbol{<} \gdef\latticeLessEqualSymbol{\le} \gdef\posetGreaterSymbol{>} \gdef\posetGreaterEqualSymbol{\ge} \gdef\posetLessSymbol{<} \gdef\posetLessEqualSymbol{\le} \gdef\posetCoversSymbol{⋗} \gdef\posetCoveredBySymbol{⋖} \gdef\grpname#1{\operatorname{\mathsf{#1}}} \gdef\mkg#1#2#3{\grpname{#1}({#2},{#3})} \gdef\mka#1#2#3{\mathfrak{#1}({#2},{#3})} \gdef\generalLinearAlgebra#1#2{\mka{gl}{#1}{#2}} \gdef\generalLinearGroup#1#2{\mkg{GL}{#1}{#2}} \gdef\specialLinearAlgebra#1#2{\mka{sl}{#1}{#2}} \gdef\specialLinearGroup#1#2{\mkg{SL}{#1}{#2}} \gdef\projectiveGeneralLinearAlgebra#1#2{\mka{pgl}{#1}{#2}} \gdef\projectiveGeneralLinearGroup#1#2{\mkg{PGL}{#1}{#2}} \gdef\projectiveSpecialLinearAlgebra#1#2{\mka{psl}{#1}{#2}} \gdef\projectiveSpecialLinearGroup#1#2{\mkg{PSL}{#1}{#2}} \gdef\orthogonalAlgebra#1#2{\mka{o}{#1}{#2}} \gdef\orthogonalGroup#1#2{\mkg{O}{#1}{#2}} \gdef\specialOrthogonalAlgebra#1#2{\mka{so}{#1}{#2}} \gdef\specialOrthogonalGroup#1#2{\mkg{SO}{#1}{#2}} \gdef\unitaryAlgebra#1{\mka{u}{#1}{#2}} \gdef\unitaryGroup#1{\mkg{U}{#1}{#2}} \gdef\specialUnitaryAlgebra#1#2{\mka{su}{#1}{#2}} \gdef\specialUnitaryGroup#1#2{\mkg{su}{#1}{#2}} \gdef\spinAlgebra#1#2{\mka{spin}{#1}{#2}} \gdef\spinGroup#1#2{\mkg{Spin}{#1}{#2}} \gdef\pinAlgebra#1#2{\mka{pin}{#1}{#2}} \gdef\pinGroup#1#2{\mkg{Pin}{#1}{#2}} \gdef\symmetricGroup#1{\grpname{Sym}({#1})} \gdef\presentation#1{#1} \gdef\groupPresentation#1#2{\left\langle\,{#1}\,\,\middle|\mathstrut\,\,{#2}\,\right\rangle} \gdef\groupRelationIso{=} \gdef\groupGenerator#1{#1} \gdef\groupRelator#1{#1} \gdef\groupElement#1{#1} \gdef\identityElement#1{#1} \gdef\groupoidElement#1{#1} \gdef\groupIdentity#1{#1} \gdef\groupoidIdentityElement#1#2{#1_{#2}} \gdef\ringIdentity#1{#1} \gdef\iconstruct#1#2{{#1}\,\,\middle|{\large\mathstrut}\,\,{#2}} \gdef\setConstructor#1#2{\left\{\,\iconstruct{#1}{#2}\,\right\}} \gdef\multisetConstructor#1#2{\left\{\mkern{-2.3pt}\left|\,\,\iconstruct{#1}{#2}\,\right|\mkern{-2.3pt}\right\}} \gdef\cardinalityConstructor#1#2{\left|\,\iconstruct{#1}{#2}\,\right|} \gdef\setToMultiset#1{{#1}^\uparrow} \gdef\multisetToSet#1{{#1}^\downarrow} \gdef\subsets#1{\setLetter({#1})} \gdef\signedSubsets#1{\signedSetLetter({#1})} \gdef\multisets#1{\multisetLetter({#1})} \gdef\signedMultisets#1{\signedMultisetLetter({#1})} \gdef\circleSpaceSymbol{S} \gdef\topologicalSpace#1{#1} \gdef\bundleSection#1{#1} \gdef\bundleProjection#1{#1} \gdef\setSymbol#1{#1} \gdef\signedSetSymbol#1{#1} \gdef\multisetSymbol#1{#1} \gdef\signedMultisetSymbol#1{#1} \gdef\setElementSymbol#1{#1} \gdef\signedSetElementSymbol#1{#1} \gdef\multisetElementSymbol#1{#1} \gdef\signedMultisetElementSymbol#1{#1} \gdef\negated#1{\bar{#1}} \gdef\positiveSignedPart#1{{#1}^+} \gdef\negativeSignedPart#1{{#1}^-} \gdef\multisetMultiplicitySymbol{\,\raisebox{.1em}{\small\#}\mkern{.1em}\,} \gdef\signedMultisetMultiplicitySymbol{\,\raisebox{.1em}{\small\#}\mkern{.1em}\,} \gdef\boundMultiplicityFunction#1{{#1}^{\sharp}} \gdef\boundSignedMultiplicityFunction#1{\operatorname{{#1}^{\sharp}}} \gdef\constructor#1#2{\left.{#1}\,\,\middle|\mathstrut\,\,{#2}\right.} \gdef\elemOf#1#2{{ {#1} \in {#2} }} \gdef\notElemOf#1#2{{ {#1} \notin {#2} }} \gdef\edgeOf#1#2{{ {#1} {\in}_E {#2} }} \gdef\vertOf#1#2{{ {#1} {\in}_V {#2} }} \gdef\pathOf#1#2{{ {#1} {\in}_P {#2} }} \gdef\pathType#1{\operatorName{path}{#1}} \gdef\vertexType#1{\operatorName{vertex}{#1}} \gdef\edgeType#1{\operatorName{edge}{#1}} \gdef\multisetType#1{\operatorName{mset}{#1}} \gdef\signedMultisetType#1{\operatorName{mset^*}{#1}} \gdef\submset{\mathbin{\dot{\subset}}} \gdef\submseteq{\mathbin{\dot{\subseteq}}} \gdef\supmset{\mathbin{\dot{\supset}}} \gdef\supmseteq{\mathbin{\dot{\supseteq}}} \gdef\unitInterval{\mathbb{I}} \gdef\fromTo#1{#1} \gdef\fromToSymbol{\mapsto} \gdef\vertexCountOf#1{|{#1}|} \gdef\vertices#1{ V_{#1} } \gdef\edges#1{ E_{#1} } \gdef\vertexField#1{#1} \gdef\edgeField#1{#1} \gdef\pathVector#1{\mathbf{#1}} \gdef\pathVectorSpace#1{\mathscr{#1}} \gdef\baseField#1{#1} \gdef\finiteField#1{\mathbb{F}_{#1}} \gdef\functionSpace#1#2{#2^{#1}} \gdef\finiteTotalFunctionSpace#1#2{#2^{\sub #1}} \gdef\pathGroupoid#1{{ \Gamma_{#1} }} \gdef\forwardPathQuiver#1#2{{\overrightharpoon{#1}_{#2}}} \gdef\backwardPathQuiver#1#2{{\overrightharpoon{#1}^{#2}}} \gdef\pathQuiver#1{{\overrightharpoon{#1}}} \gdef\mto#1#2{{#1}\mapsto{#2}} \gdef\mtoSymbol{\mapsto} \gdef\groupWordRewriting#1{\langle{#1}\rangle} \gdef\rewrite#1#2{{#1}\mapsto{#2}} \gdef\rewritingRule#1#2{{#1}\mapsto{#2}} \gdef\rewritingSystem#1{\mathcal{#1}} \gdef\multiwayBFS#1{\textrm{bfs}({#1})} \gdef\rewritingStateBinding#1#2{{\left.{#1}\!\mid\!{#2}\right.}} \gdef\rewritingRuleBinding#1#2{#1{\left[\,{#2}\,\right]}} \gdef\namedSystem#1{\mathtt{#1}} \gdef\genericRewritingSystem{\namedSystem{Sys}} \gdef\stringRewritingSystem{\namedSystem{Str}} \gdef\circularStringRewritingSystem{\namedSystem{CStr}} \gdef\turingMachineRewritingSystem{\namedSystem{TM}} \gdef\cellularAutomatonRewritingSystem{\namedSystem{CA}} \gdef\graphRewritingSystem{\namedSystem{Gr}} \gdef\hypergraphRewritingSystem{\namedSystem{HGr}} \gdef\petriNetRewritingSystem{\namedSystem{Petri}} \gdef\localStates#1{\localStatesSymbol^#1} \gdef\regionalStates#1{\regionalStatesSymbol^#1} \gdef\globalStates#1{\globalStatesSymbol^#1} \gdef\keySubStates#1{\keySubStatesSymbol^#1} \gdef\valueSubStates#1{\valueSubStatesSymbol^#1} \gdef\localState#1#2{#2_{#1}} \gdef\regionalState#1{#1} \gdef\globalState#1{#1} \gdef\keySubState#1{#1} \gdef\valueSubState#1{#1} \gdef\lhsState#1{#1_{L}} \gdef\rhsState#1{#1_{R}} \gdef\rewriteLHSRegionalState#1{#1_{L}} \gdef\rewriteRHSRegionalState#1{#1_{R}} \gdef\regionalStateForm#1{\daGFo{(}#1\daGFo{)}} \gdef\invalidRegionalState{\reFo{\times}} \gdef\emptyRegionalState{\regionalStateForm{}} \gdef\regionalSubstateSymbol{\sqsubseteq} \gdef\regionalSuperstateSymbol{\sqsupseteq} \gdef\comparableRegionalStatesSymbol{\mathbin{\square}} \gdef\incomparableRegionalStatesSymbol{\mathbin{\boxtimes}} \gdef\namedStateSet#1{\mathbf #1} \gdef\localStatesSymbol{\namedStateSet L} \gdef\regionalStatesSymbol{\namedStateSet R} \gdef\globalStatesSymbol{\namedStateSet G} \gdef\keySubStatesSymbol{\namedStateSet L_K} \gdef\valueSubStatesSymbol{\namedStateSet L_V} \gdef\localStateSymbol#1{#1} \gdef\regionalStateSymbol#1{#1} \gdef\globalStateSymbol#1{#1} \gdef\keySubStateSymbol#1{#1} \gdef\valueSubStateSymbol#1{#1} \gdef\infixComposeLocalStatesSymbol{\_} \gdef\composeLocalStatesSymbol{\operatorname{glue}} \gdef\composeLocalStatesForm#1{\composeLocalStatesSymbol(#1)} \gdef\ncard#1{\card{\inverted{#1}}} \gdef\mcard#1{\card{\mirror{#1}}} \gdef\nmcard#1{\card{\inverted{\mirror{#1}}}} \gdef\assocArray#1{\left\langle {#1} \right\rangle} \gdef\openMultiset{\lBrace} \gdef\closeMultiset{\rBrace} \gdef\set#1{\{ {#1} \}} \gdef\signedSet#1{\{ {#1} \}} \gdef\list#1{\{ {#1} \}} \gdef\multiset#1{\openMultiset {#1} \closeMultiset} \gdef\signedMultiset#1{\openMultiset {#1} \closeMultiset} \gdef\styledSet#1#2{#1\{ {#1} #1\}} \gdef\styledList#1#2{#1\{ {#1} #1\}} \gdef\styledMultiset#1#2{#1\openMultiset {#2} #1\closeMultiset} \gdef\styledSignedMultiset#1#2{\openMultiset {#2} \closeMultiset} \gdef\permutationCycle#1{#1} \gdef\permutationCycleSymbol{\to} \gdef\permutationSet#1{#1} \gdef\permutationSetSymbol{;} \gdef\transposition#1#2{{#1} \leftrightarrow {#2}} \gdef\tuple#1{( {#1} )} \gdef\concat#1{ {#1} } \gdef\paren#1{\left( {#1} \right)} \gdef\ceiling#1{\lceil{#1}\rceil} \gdef\floor#1{\lfloor{#1}\rfloor} \gdef\translationVector#1{\left[{#1}\right]_{\textrm{T}}} \gdef\quotient#1#2{{#1} / {#2}} \gdef\compactQuotient#1#2#3{{#1}\;{\upharpoonright_{#2}}\;{#3}} \gdef\multilineQuotient#1#2{\frac{#1}{#2}} \gdef\idElem#1{e_{#1}} \gdef\minus#1{-{#1}} \gdef\elem{\ \in\ } \gdef\vsp{\mkern{0.4pt}} \gdef\iGmult{\vsp} \gdef\gmult{\vsp\ast\vsp} \gdef\Gmult{\vsp\ast\vsp} \gdef\gdot{\vsp\cdot\vsp} \gdef\gDot{\vsp\mathbin{\largeDot}\vsp} \gdef\mdot{\vsp\cdot\vsp} \gdef\smallblackcirc{\vsp\raisebox{0.15em}{\tiny∙}\vsp} \gdef\smallwhitecirc{\vsp\raisebox{0.15em}{\tiny∘}\vsp} \gdef\sgdot{\mathbin{\smallwhitecirc}} \gdef\srdot{\mathbin{\smallblackcirc}} \gdef\srplus{+} \gdef\verticalEllipsis{\vdots} \gdef\appliedRelation#1{#1} \gdef\setUnionSymbol{\cup} \gdef\setIntersectionSymbol{\cap} \gdef\setRelativeComplementSymbol{-} \gdef\msetCol{\textcolor{bb4444}} \gdef\repeatedMultiset#1#2{#1\,#2} \gdef\msrdot{\mathbin{\smallblackcirc}} \gdef\msrplus{+} \gdef\smrdot{\mathbin{\smallblackcirc}} \gdef\smrplus{+} \gdef\dotminus{\mathbin{\dot{-}}} \gdef\dotcap{\mathbin{\dot{\cap}}} \gdef\dotcup{\mathbin{\dot{\cup}}} \gdef\multisetUnionSymbol{\dotcup} \gdef\multisetIntersectionSymbol{\dotcap} \gdef\multisetRelativeComplementSymbol{\dotminus} \gdef\multisetSumSymbol{\dotplus} \gdef\cartesianProductSymbol{\times} \gdef\functionType#1#2{{#1} \to {#2}} \gdef\functionSignature#1#2#3{{{#1} : {#2} \to {#3}}} \gdef\partialFunctionSignature#1#2#3{{{#1} : {#2} \rightharpoonup {#3}}} \gdef\poly#1{#1} \gdef\quiverProdPoly#1{#1} \gdef\quiverProdPower#1#2{#1^{#2}} \gdef\quiverProdTimes#1{#1} \gdef\parenLabeled#1#2{#1\ ({#2})} \gdef\parenRepeated#1#2{\parenLabeled{#1}{{#2}\text{ times}}} \gdef\underLabeled#1#2{\underbrace{#1}_{#2}} \gdef\underRepeated#1#2{\underbrace{#1}_{#2\text{ times}}} \gdef\overLabeled#1#2{\overbrace{#1}^{#2}} \gdef\overRepeated#1#2{\overbrace{#1}^{#2\text{ times}}} \gdef\modLabeled#1#2{{#1 }\textrm{ mod }{#2}} \gdef\freeGroup#1{F_{#1}} \gdef\cyclicGroup#1{\mathbb{Z}_{#1}} \gdef\componentSuperQuiverOfSymbol{\succ} \gdef\setCardinality#1{|{#1}|} \gdef\multisetCardinality#1{|{#1}|} \gdef\dependentQuiverProductSymbol{\mathbin{\times}} \gdef\rightIndependentQuiverProductSymbol{\mathbin{⋊}} \gdef\leftIndependentQuiverProductSymbol{\mathbin{⋉}} \gdef\rightStrongQuiverProductSymbol{\mathbin{⧒}} \gdef\leftStrongQuiverProductSymbol{\mathbin{⧑}} \gdef\rightFiberQuiverProductSymbol{\mathbin{⧕}} \gdef\leftFiberQuiverProductSymbol{\mathbin{⧔}} \gdef\lockedQuiverProductSymbol{\mathbin{\searrow}} \gdef\rightFreeQuiverProductSymbol{\mathbin{\smallerthan}} \gdef\leftFreeQuiverProductSymbol{\mathbin{\largerthan}} \gdef\strongIndependentQuiverProductSymbol{\mathbin{⨝}} \gdef\cartesianQuiverProductSymbol{\mathbin{□}} \gdef\strongQuiverProductSymbol{\mathbin{⊠}} \gdef\graphUnionSymbol{\sqcup} \gdef\graphProductSymbol{\times} \gdef\inlineProdSymbol{|} \gdef\serialCardSymbol{{:}} \gdef\parallelCardSymbol{{\mid}} \gdef\cardinalSequenceSymbol{{:}} \gdef\cardinalProduct#1{(#1)} \gdef\vertexProduct#1{(#1)} \gdef\edgeProduct#1{(#1)} \gdef\cardinalProductSymbol{\inlineProdSymbol} \gdef\vertexProductSymbol{\inlineProdSymbol} \gdef\edgeProductSymbol{\inlineProdSymbol} \gdef\verticalVertexProduct#1#2{\cfrac{#1}{#2}} \gdef\verticalCardinalProduct#1#2{\cfrac{#1}{#2}} \gdef\indexSum#1#2#3{{\sum_{#2}^{#3} #1}} \gdef\indexProd#1#2#3{{\prod_{#2}^{#3} #1}} \gdef\indexMax#1#2#3{{\max_{#2}^{#3} #1}} \gdef\indexMin#1#2#3{{\min_{#2}^{#3} #1}} \gdef\indexUnion#1#2#3{{\bigcup_{#2}^{#3} #1}} \gdef\indexIntersection#1#2#3{{\bigcap_{#2}^{#3} #1}} \gdef\indexGraphUnion#1#2#3{{\bigcup_{#2}^{#3} #1}} \gdef\indexGraphDisjointUnion#1#2#3{{\bigcup_{#2}^{#3} #1}} \gdef\styledIndexSum#1#2#3#4{{#1\sum_{#3}^{#4} #2}} \gdef\styledIndexProd#1#2#3#4{{#1\prod_{#3}^{#4} #2}} \gdef\styledIndexMax#1#2#3#4{{#1\max_{#3}^{#4} #2}} \gdef\styledIndexMin#1#2#3#4{{#1\min_{#3}^{#4} #2}} \gdef\indexSumSymbol{\sum} \gdef\indexProdSymbol{\prod} \gdef\indexMaxSymbol{\max} \gdef\indexMinSymbol{\min} \gdef\openInterval#1#2{(#1,#2)} \gdef\closedInterval#1#2{[#1,#2]} \gdef\openClosedInterval#1#2{(#1,#2]} \gdef\closedOpenInterval#1#2{[#1,#2)} \gdef\oneTo#1{1..{#1}} \gdef\zeroTo#1{0..{#1}} \gdef\qstring#1{\mathtt{"}{#1}\mathtt{"}} \gdef\wstring#1{\textcolor{6b6b6b}{#1}} \gdef\qchar#1{\mathtt{'}{#1}\mathtt{'}} \gdef\lstr#1{\mathtt{#1}} \gdef\lchar#1{\mathtt{#1}} \gdef\string#1{{#1}} \gdef\character#1{{#1}} \gdef\homomorphismMapping#1{\assocArray{#1}} \gdef\starModifier#1{{#1}^*} \gdef\translationPresentation#1{\textrm{Z}_{#1}} \gdef\starTranslationPresentation#1{\textrm{Z}^*_{#1}} \gdef\translationPathValuation#1{\mathcal{\overrightharpoon Z}_{#1}} \gdef\starTranslationPathValuation#1{\overrightharpoon{\mathcal{Z}^*_{#1}}} \gdef\translationWordHomomorphism#1{\mathcal{Z}_{#1}} \gdef\starTranslationWordHomomorphism#1{\mathcal{Z}^*_{#1}} \gdef\translationCardinalValuation#1{\textrm{T}_{#1}} \gdef\starTranslationCardinalValuation#1{\textrm{T}^*_{#1}} \gdef\reFo#1{\textcolor{e1432d}{#1}} \gdef\grFo#1{\textcolor{4ea82a}{#1}} \gdef\blFo#1{\textcolor{3e81c3}{#1}} \gdef\orFo#1{\textcolor{dc841a}{#1}} \gdef\piFo#1{\textcolor{c74883}{#1}} \gdef\teFo#1{\textcolor{47a5a7}{#1}} \gdef\gFo#1{\textcolor{929292}{#1}} \gdef\puFo#1{\textcolor{8b7ebe}{#1}} \gdef\liReFo#1{\textcolor{ff775e}{#1}} \gdef\liGrFo#1{\textcolor{82dd63}{#1}} \gdef\liBlFo#1{\textcolor{6caff4}{#1}} \gdef\liOrFo#1{\textcolor{ffbb5f}{#1}} \gdef\liPiFo#1{\textcolor{fb77b0}{#1}} \gdef\liTeFo#1{\textcolor{7fdbdc}{#1}} \gdef\liGFo#1{\textcolor{c5c5c5}{#1}} \gdef\liPuFo#1{\textcolor{bbaff2}{#1}} \gdef\daReFo#1{\textcolor{b50700}{#1}} \gdef\daGrFo#1{\textcolor{217f00}{#1}} \gdef\daBlFo#1{\textcolor{165e9d}{#1}} \gdef\daOrFo#1{\textcolor{ae5900}{#1}} \gdef\daPiFo#1{\textcolor{9e1f61}{#1}} \gdef\daTeFo#1{\textcolor{0e7c7e}{#1}} \gdef\daGFo#1{\textcolor{6b6b6b}{#1}} \gdef\daPuFo#1{\textcolor{665996}{#1}} \gdef\boFo#1{\mathbf{#1}} \gdef\itFo#1{\mathit{#1}} \gdef\unFo#1{\underline{#1}} \gdef\stFo#1{\struckthrough{#1}} \gdef\plTeFo#1{\textrm{#1}} \gdef\maTeFo#1{\textrm{#1}} \gdef\ZNFuFo#1{\operatorname{#1}} \gdef\ZAFo#1#2{#1(#2)} \gdef\noApSy{\gFo{\text{---}}} \gdef\unSy{\gFo{?}} \gdef\emSeSy{\gFo{ \emptyset }} \gdef\tiSy{\boFo{ \vthinspace ✓ \vthinspace }} \gdef\unIn{\mathbb{I}} \gdef\blSy{\gFo{\_}} \gdef\plSqSy{□} \gdef\baToSy{\boFo{ \vthinspace | \vthinspace }} \gdef\fiToSy{●} \gdef\fiSqToSy{■} \gdef\fiReToSy{▮} \gdef\emToSy{○} \gdef\emSqToSy{□} \gdef\emReToSy{▯} \gdef\plElSy{\,...\,} \gdef\ceElSy{\,\cdot\!\cdot\!\cdot\,} \gdef\elSy{\,\gFo{...}\,} \gdef\veElSy{\vdots} \gdef\coFo{\sqsubseteq} \gdef\CoFo#1#2{#1 \coFo #2} \gdef\coByFo{⊑} \gdef\CoByFo#1#2{#1 \coByFo #2} \gdef\stCoFo{\sqsupset} \gdef\StCoFo#1#2{#1 \stCoFo #2} \gdef\stCoByFo{\sqsubset} \gdef\StCoByFo#1#2{#1 \stCoByFo #2} \gdef\inCoFo{\sqsubseteq} \gdef\InCoFo#1#2{#1 \inCoFo #2} \gdef\InCoFoⅡ#1#2#3{#1 \inCoFo_{#3} #2} \gdef\grInCoFo{\sqsubseteq} \gdef\GrInCoFo#1#2{#1 \grInCoFo #2} \gdef\GrInCoFoⅡ#1#2#3{#1 \grInCoFo_{#3} #2} \gdef\quInCoFo{\sqsubseteq} \gdef\QuInCoFo#1#2{#1 \quInCoFo #2} \gdef\QuInCoFoⅡ#1#2#3{#1 \quInCoFo_{#3} #2} \gdef\coPrFo{\cdot} \gdef\CoPrFo#1{#1} \gdef\coSuFo{\sqcup} \gdef\CoSuFo#1{#1} \gdef\isCoFo{\sim} \gdef\IsCoFo#1#2{#1 \isCoFo #2} \gdef\IsCoFoⅡ#1#2#3{#1 \isCoFo_{#3} #2} \gdef\isNoCoFo{\nsim} \gdef\IsNoCoFo#1#2{#1 \isNoCoFo #2} \gdef\IsNoCoFoⅡ#1#2#3{#1 \isNoCoFo_{#3} #2} \gdef\coReFo{\sim} \gdef\CoReFo#1{#1} \gdef\TuFo#1{(#1)} \gdef\SeFo#1{{#1}} \gdef\StSeFo#1#2#3{#1#3#2} \gdef\inArSy{⏵} \gdef\arSy{⏴} \gdef\upArSy{⏶} \gdef\doArSy{⏷} \gdef\leArSy{⏴} \gdef\riArSy{⏵} \gdef\grAuFu{\operatorname{Aut}} \gdef\PaFo#1{\;#1\;} \gdef\na{\mathbb{n}} \gdef\poNa{\mathbb{N} ^+} \gdef\poRe{\mathbb{R} ^+} \gdef\pr{\mathbb{P}} \gdef\re{\mathbb{R}} \gdef\piSy{\pi} \gdef\taSy{\tau}\]

Summary and roadmap #

Overall summary #

Here is a brief summary of what has been achieved so far.

The main object we consider is the cardinal quiver, a locally finite directed multigraph with shared oriented edge labels called cardinals. (We abbreviate cardinal quiver as quiver.)

Important examples of quivers are given by the Cayley quivers of Abelian groups, which can also be constructed as quotients. We can generalize these constructions by considering group actions, more complex quotients, cyclic groups, and non-Abelian groups.

Notice that the connection with groups via action quivers is especially important, because it provides a kind of Rosetta stone to port intuition back and forth between quivers and groups. The general idea will be that quivers provide a way of handling partial symmetries of structures that elude modelling by groups.

Additional examples of quivers come directly from the causal structure of a non-deterministic computation, as expressed by a rewriting system.

The paths on a quiver form a groupoid called the path groupoid. Maps between path groupoids yield path homomorphisms. Surjective path homomorphisms yield a notion of covering, coverings form a lattice and are associated with transitive vertex colorings in certain cases.

We can form products of quivers, allowing us to derive new quivers from old ones, giving as alternative ways of constructing the square and triangular quivers. We can form some intransitive quivers like the hexagonal quiver. Using these products we can define the local trivializations needed for a discrete notion of a fiber bundle.

More complex quivers can be partitioned into charts in which particular path relations hold, the connectivity of these charts is described by another quiver. A notion of parallel transport analogous to the Ehresmann connection can be defined that relates cardinals on different charts. Curvature is described by holonomy on this derived quiver. We can compute the curvature of a quiver for the Möbius strip.

Roadmap #

This project continues to evolve and certain sections are either out of date or underdeveloped. Here I list some limitations and planned improvements for certain existing sections, and new sections that are on the roadmap.

Hypergraphs and hyperquivers #

Hypergraphs lack a nice ontology in the traditional mathematical literature. One can be given in terms of type theory -- multisets play a crucial role.

Why do we need hypergraphs? They are, I suspect, far more pervasive than graphs in pure and applied contexts -- but the lack of mathematical maturity in the abstract theory of hypergraphs means the common structure has been left latent more often than not.

Path homomorphisms #

The section Path homomorphisms gives a good introduction to homomorphisms between quivers, but fails to explain the notion of topology that they induce. There is also low-hanging fruit to pick, like explaining the role of exact sequences.

Topology #

As mentioned above, interpreting path homomorphisms between quivers as continuous maps implies a natural topological structure on the associated quivers. A section is needed to unpack this fully.

Symmetry #

I am missing the obvious section on symmetry that would build on affine path homomorphisms to recover the isometry and isotropy groups of the associated crystallographic lattices in the case of lattice quivers. This will be straightforward, but the connection with hypergroups, especially for non-transitive lattices, is much more interesting, and unexplored.

Non-commutativity #

The section Noncommutativity is currently just a stub. Careful study needs to be made of action quivers associated to the non-Abelian groups, and a link forged with a forthcoming section on Lie algebras.

Quiver products #

The section Quiver products could do with some more discussion of the algebraic aspects of arrow polynomials. In particular I need to explain the operad structure precisely, as well as formalize the polynomials themselves as a ring acting on a quivers that are also valued in a (semi)ring -- this perspective demands a proper treatment of quivers (and hyperquivers) as multiset-based data structures. There is also a fairly obvious connection between arrow polynomials to the path representations used in Lattice quivers, but this will require path representations to be rephrased in terms of modular representations to be made more complete.

Fiber bundles #

This section is incomplete, it mostly just recaps that traditional notion of fiber bundles of topological spaces. The description of discrete fiber bundles is still under construction. It is crucial for other definitions, in particular of curvature, which will be similar to the approach used by Manton.

Rewriting systems #

The section Rewriting systems develops some of the ideas of how formalize the lattice of states, but needs many more examples before engaging in this formalization, which may be premature anyway. It should be split into two sections, one for examples and the second for partial state.

Nevertheless, the overall theoretical program is as follows: a rewriting system generates a rewrite quiver that describes its transitions, with the cardinal structure identifying rewrites of unique substates of the global state. Forward paths through this quiver correspond to possible evolutions of the system. Re-ordering of causally distinct rewrites (“rewrites that commute”) defines a homotopy relation between such paths, taking us between evolutions that differ in the time foliation of something called the rewrite hypergraph -- which factors local states.

The generators of these reorderings form the cardinals of a quiver analogous to the Lorentz group. In this sense we can construct a computational analogue of Special Relativity, but with the appropriate quiver-theoretic tools to model the partial symmetry that discrete systems manifest.

Contraction lattices #

The section Contraction lattices describes how contractions of a quiver form an order-theoretic lattice, but doesn't probe any of the interesting properties of this lattice in general or for particular quivers. Crucially it doesn't answer when the lattices are distributive or modular, when they satisfy the descending or ascending chain conditions, and make links between these properties and the associated algebraic properties of the path ring.

Curvature #

The section Cardinal transport proposes a definition of discrete curvature that is not as precise as it should be. It suffers from the lack of a quiver-theoretic notion of a (principle) fiber bundle and tangent bundle. Doing this would allow definition of curvature in terms of homology. The fiber we require is the Cayley quiver of a signed permutation group that represents possible rewrites.

Defects #

Curvature in the quiver-theoretic picture is fully determined by the the presence of "defects". I haven't touched on these defects in any meaningful way, enumerated them, created a language to describe them computationally, demonstrated how certain computations produce them, perform calculus in the presence of them, and so on.

Tangent bundles #

As mentioned above, the definition of curvature on a quiver is unsatisfactory. Currently, the transport atlas is defined as a quiver whose edges describe transitions between charts, where these edges are labeled with cardinal rewrites that capture cardinal transport. A more flexible construction would be to define the curvature quiver as a subquiver that corresponds to a section of a fibre bundle, where the fibre quiver is the Cayley quiver of a signed permutation group. This would allow us to define curvature via homology.

Metrics #

The familiar graph distance metric, which for Cayley quivers corresponds to the word metric in the associated group presentation, has many undesirable properties. For example, it is not isotropic. Intriguingly, the theory of random walks on graphs can recover the Euclidean metric defined by the obvious embedding of the associated quivers into \( \realVectorSpace{\sym{n}} \). Developing this idea, particularly in connection with information theory and quiver contractions, is a high priority.

Geometric algebra #

Geometric algebra provides a novel way to model many familiar constructs in geometry and physics by way of bivectors, multivectors, etc. I'm not sure what form geometric algebra would naturally take in quiver geometry, but I'm highly motivated to pursue this.

Abstract algebra #

There is reason to believe that abstract algebra will have a lot to say about the path ring, but I haven't devoted enough time to thinking about this.

Presentation #

I plan to improve the overall presentation of these ideas in the following ways:

Video #

I'd like to make some short videos that introduce the main ideas in an easy-going way, with plenty of illustrative examples.

Symbols #

I use KaTeX in such a way that the roles of individual symbols are known: whether a given symbol represents a group, ring, quiver, path homomorphism, etc. I'd like to surface this information using some kind of interactive mechanism or legend, to make it easier for readers to parse complicated expressions when they are in doubt.

Material #

This website is generated from a series of Mathematica notebooks using custom tooling. While all the underlying software tools I use are available on Github. Unfortunately, the storage format of notebooks is ill-suited to version control, so the notebooks themselves are not public. I'd like to fix this by moving to a purely markdown-based storage format.

References #

I don't have any references anywhere! Most urgently I need to root into the literature on crystallographic groups, geometric group theory, and differential geometry.

Category theory #

I do not meaningfully engage with category theory yet. Using category theory widely would bring simplifications to the overall conceptual structure, but make the material more alienating to those without the requisite background. I'd like to experiment with gated content, in which you can flip between versions of the site that are tailored for different audiences.