diff -r 4d0ca2fc4f2b -r 86c8e2129355 text/appendixes/comparing_defs.tex --- a/text/appendixes/comparing_defs.tex Thu Jul 22 16:16:58 2010 -0600 +++ b/text/appendixes/comparing_defs.tex Thu Jul 22 19:32:40 2010 -0600 @@ -207,7 +207,59 @@ \subsection{$A_\infty$ $1$-categories} \label{sec:comparing-A-infty} In this section, we make contact between the usual definition of an $A_\infty$ category -and our definition of a topological $A_\infty$ $1$-category, from \S \ref{???}. +and our definition of a topological $A_\infty$ $1$-category, from \S \ref{ss:n-cat-def}. + +\medskip + +Given a topological $A_\infty$ $1$-category $\cC$, we define an ``$m_k$-style +$A_\infty$ $1$-category $A$ as follows. +The objects of $A$ are $\cC(pt)$. +The morphisms of $A$, from $x$ to $y$, are $\cC(I; x, y)$ +($\cC$ applied to the standard interval with boundary labeled by $x$ and $y$). +For simplicity we will now assume there is only one object and suppress it from the notation. + +A choice of homeomorphism $I\cup I \to I$ induces a chain map $m_2: A\times A\to A$. +We now have two different homeomorphisms $I\cup I\cup I \to I$, but they are isotopic. +Choose a specific 1-parameter family of homeomorphisms connecting them; this induces +a degree 1 chain homotopy $m_3:A\ot A\ot A\to A$. +Proceeding in this way we define the rest of the $m_i$'s. +It is straightforward to verify that they satisfy the necessary identities. + +\medskip + +In the other direction, we start with an alternative conventional definition of an $A_\infty$ algebra: +an algebra $A$ for the $A_\infty$ operad. +(For simplicity, we are assuming our $A_\infty$ 1-category has only one object.) +We are free to choose any operad with contractible spaces, so we choose the operad +whose $k$-th space is the space of decompositions of the standard interval $I$ into $k$ +parameterized copies of $I$. +Note in particular that when $k=1$ this implies a $\Homeo(I)$ action on $A$. +(Compare with Example \ref{ex:e-n-alg} and preceding discussion.) +Given a non-standard interval $J$, we define $\cC(J)$ to be +$(\Homeo(I\to J) \times A)/\Homeo(I\to I)$, +where $\beta \in \Homeo(I\to I)$ acts via $(f, a) \mapsto (f\circ \beta\inv, \beta_*(a))$. +\nn{check this} +We define a $\Homeo(J)$ action on $\cC(J)$ via $g_*(f, a) = (g\circ f, a)$. +The $C_*(\Homeo(J))$ action is defined similarly. + +Let $J_1$ and $J_2$ be intervals. +We must define a map $\cC(J_1)\ot\cC(J_2)\to\cC(J_1\cup J_2)$. +Choose a homeomorphism $g:I\to J_1\cup J_2$. +Let $(f_i, a_i)\in \cC(J_i)$. +We have a parameterized decomposition of $I$ into two intervals given by +$g\inv \circ f_i$, $i=1,2$. +Corresponding to this decomposition the operad action gives a map $\mu: A\ot A\to A$. +Define the gluing map to send $(f_1, a_1)\ot (f_2, a_2)$ to $(g, \mu(a_1\ot a_2))$. + +It is straightforward to verify the remaining axioms for a topological $A_\infty$ 1-category. + + + + + + + +\noop { %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% That definition associates a chain complex to every interval, and we begin by giving an alternative definition that is entirely in terms of the chain complex associated to the standard interval $[0,1]$. \begin{defn} @@ -299,4 +351,6 @@ as required (c.f. \cite[p. 6]{MR1854636}). \todo{then the general case.} We won't describe a reverse construction (producing a topological $A_\infty$ category -from a ``conventional" $A_\infty$ category), but we presume that this will be easy for the experts. \ No newline at end of file +from a ``conventional" $A_\infty$ category), but we presume that this will be easy for the experts. + +} %%%%% end \noop %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \ No newline at end of file