diff --git a/Notes/smash.tex b/Notes/smash.tex index ec01b0b..475ab18 100644 --- a/Notes/smash.tex +++ b/Notes/smash.tex @@ -191,7 +191,7 @@ f'\smash 0\arrow[dl,equals] \\ (a_3,b_3) \end{tikzcd} \end{center} - + If $x$ varies over $\gluer_b$, we need to fill the cube below. The front and the back are the squares we just filled, the left square is a degenerate square, and the other three squares are the squares in the definition of $q$ and $i$ to show that they respect $\gluer_b$ (and on the @@ -211,7 +211,7 @@ f'\smash 0\arrow[dl,equals] \\ After canceling applications of $\mapfunc{h\smash k}(\gluer_z)=\gluer_{k(z)}$ on various sides of the squares (TODO). - + If $x$ varies over $\gluel_a$ the proof is very similar. Only in the end we need to fill the following cube instead (TODO). @@ -222,12 +222,9 @@ f'\smash 0\arrow[dl,equals] \\ \begin{thm}\label{thm:smash-functor-right} Given pointed types $A$, $B$ and $C$, the functorial action of the smash product induces a map $$({-})\smash C:(A\pmap B)\pmap(A\smash C\pmap B\smash C)$$ -which is natural in $A$, $B$ and $C$. (note: $(A\smash C\pmap B\smash C)$ is both covariant and contravariant in $C$). +which is natural in $A$, $B$ and dinatural in $C$. \end{thm} -\begin{proof} - First note that $\lam{f}f\smash C$ preserves the basepoint so that the map is indeed pointed. We - show that this map is natural in each of its arguments individually, which means we need to fill - the following squares for $f : A' \to A$ $g:B\to B'$ and $h:C\to C'$. +The naturality and dinaturality means that the following squares commute for $f : A' \to A$ $g:B\to B'$ and $h:C\to C'$. \begin{center} \begin{tikzcd} (A\pmap B) \arrow[r,"({-})\smash C"]\arrow[d,"f\pmap B"] & @@ -248,10 +245,13 @@ which is natural in $A$, $B$ and $C$. (note: $(A\smash C\pmap B\smash C)$ is bot (A\smash C\pmap B\smash C') \end{tikzcd} \end{center} +\begin{proof} +First note that $\lam{f}f\smash C$ preserves the basepoint so that the map is indeed pointed. + Let $k:A\pmap B$. Then as homotopy the naturality in $A$ becomes $(k\o f)\smash C=k\smash C\o f\smash C$. To prove an equality between pointed maps, we need to give a pointed homotopy, which is given by interchange. To show that this homotopy is pointed, we need to -fill the following square (after reducing out the applications of function extensinality), which follows from \autoref{lem:smash-coh}. +fill the following square (after reducing out the applications of function extensinality), which follows from \autoref{lem:smash-coh}. \begin{center} \begin{tikzcd} (0 \o f)\smash C \arrow[r, equals]\arrow[dd,equals] & @@ -273,21 +273,21 @@ square, which follows from \autoref{lem:smash-coh}. 0 \end{tikzcd} \end{center} -The naturality in $C$ is a bit harder. For the underlying homotopy we need to show +The dinaturality in $C$ is a bit harder. For the underlying homotopy we need to show $B\smash h\o k\smash C=k\smash C'\o A\smash h$. This follows by applying interchange twice: $$B\smash h\o k\smash C\sim(\idfunc[B]\o k)\smash(h\o\idfunc[C])\sim(k\o\idfunc[A])\smash(\idfunc[C']\o h)\sim k\smash C'\o A\smash h.$$ To show that this homotopy is pointed, we need to fill the following square: \begin{center} \begin{tikzcd} - B\smash h\o 0\smash C \arrow[r, equals]\arrow[d,equals] & + B\smash h\o 0\smash C \arrow[r, equals]\arrow[d,equals] & (\idfunc[B]\o 0)\smash(h\o\idfunc[C]) \arrow[r, equals]\arrow[d,equals] & (0\o\idfunc[A])\smash(\idfunc[C']\o h)\arrow[r, equals]\arrow[d,equals] & 0\smash C'\o A\smash h\arrow[d,equals] \\ - B\smash h\o 0 \arrow[d,equals] & + B\smash h\o 0 \arrow[d,equals] & 0\smash(h\o\idfunc[C]) \arrow[r, equals]\arrow[d,equals] & 0\smash(\idfunc[C']\o h) \arrow[d,equals] & 0\o A\smash h\arrow[d,equals] \\ - B\smash h\o 0 \arrow[r, equals] & + B\smash h\o 0 \arrow[r, equals] & 0 \arrow[r, equals] & 0 \arrow[r, equals] & 0 @@ -300,14 +300,13 @@ are filled by (corollaries of) \autoref{lem:smash-general}. \section{Adjunction} \begin{lem} - There is a unit $\eta_{A,B}\equiv\eta:A\pmap B\pmap A\smash B$ and counit - $\epsilon_{B,C}\equiv\epsilon : (B\pmap C)\smash B \pmap C$ which are natural in both arguments - and satisfy the unit-counit laws: + There is a unit $\eta_{A,B}\equiv\eta:A\pmap B\pmap A\smash B$ natural in $A$ and counit + $\epsilon_{B,C}\equiv\epsilon : (B\pmap C)\smash B \pmap C$ dinatural in $B$ and natural in $C$. + These maps satisfy the unit-counit laws: $$(A\to\epsilon_{A,B})\o \eta_{A\to B,A}\sim \idfunc[A\to B]\qquad \epsilon_{B,B\smash C}\o \eta_{A,B}\smash B\sim\idfunc[A\smash B].$$ - - \end{lem} +Note: $\eta$ is also dinatural in $B$, but we don't need this. \begin{proof} We define $\eta ab=(a,b)$. Then $\eta a$ respects the basepoint because $(a,b_0)=(a_0,b_0)$. Also, $\eta$ itself respects the basepoint. To show this, we need to show @@ -322,9 +321,9 @@ are filled by (corollaries of) \autoref{lem:smash-general}. need to show that $0(b)=c_0$ which is true by reflexivity. $\epsilon$ is trivially a pointed map, which defines the counit. - Now we need to show that the unit and counit are natural. (TODO). + Now we need to show that the unit and counit are (di)natural. (TODO). - Finally we need to show that unit-counit laws. For the underlying homotopy of the first one, let + Finally we need to show the unit-counit laws. For the underlying homotopy of the first one, let $f:A\to B$. We need to show that $p:\epsilon\o\eta f\sim f$. For the underlying homotopy of $p$, let $a:A$, and we need to show that $\epsilon(f,a)=f(a)$, which is true by reflexivity. To show that $p$ is a pointed homotopy, we need to show that @@ -401,7 +400,13 @@ $e$ is natural in $A$, $B$ and $C$. \end{tikzcd} \end{center} -\textbf{$e$ is natural in $B$}. Suppose that $f:B'\pmap B$. The diagram looks weird since $({-})\smash B$ is both contravariant and covariant in $B$. Then we get the following diagram. The front square commutes by naturality of $({-})\smash B$ in the second argument (applied to $f\pmap C$). The top square commutes by naturality of $({-})\smash B$ in the third argument, the back square commutes because composition on the left commutes with composition on the right, and finally the right square commutes by applying the functor $A\smash B' \pmap({-})$ to the naturality of $\epsilon$ in the first argument. +\textbf{$e$ is natural in $B$}. Suppose that $f:B'\pmap B$. Here the diagram is a bit more +complicated, since $({-})\smash B$ is dinatural (instead of natural) in $B$. Then we get the +following diagram. The front square commutes by naturality of $({-})\smash B$ in the second argument +(applied to $f\pmap C$). The top square commutes by naturality of $({-})\smash B$ in the third +argument, the back square commutes because composition on the left commutes with composition on the +right, and finally the right square commutes by applying the functor $A\smash B' \pmap({-})$ to the +naturality of $\epsilon$ in the first argument. \begin{center} \begin{tikzcd}[row sep=scriptsize, column sep=-4em] & (A\smash B\pmap (B\pmap C)\smash B) \arrow[rr] \arrow[dd] & & (A\smash B'\pmap (B\pmap C)\smash B)\arrow[dd] \\ @@ -422,7 +427,7 @@ $e$ is natural in $A$, $B$ and $C$. A \smash (B \smash C)\to X&\simeq A \to B\smash C\to X\\ &\simeq A \to B\to C\to X\\ &\simeq A \smash B\to C\to X\\ - &\simeq (A \smash B)\smash C\to X. + &\simeq (A \smash B)\smash C\to X. \end{align*} $\phi_X$ is natural in $A,B,C,X$ by repeatedly applying \autoref{e-natural}. Let $f\defeq\phi_{A \smash (B \smash C)}(\idfunc)$ and