more consistent punctuation

categories.tex

@@ -464,11 +464,11 @@ \section{Functors and transformations}
 We have a similar coherence result for units.
 
 \begin{lem}\label{ct:units}
-  For a functor $F:A\to B$, we have equalities $\id{(1_B\circ F)}{F}$ and $\id{(F\circ 1_A)}{F}$, such that given also $G:B\to C$, the following triangle of equalities commutes.
+  For a functor $F:A\to B$, we have equalities $\id{(1_B\circ F)}{F}$ and $\id{(F\circ 1_A)}{F}$, such that given also $G:B\to C$, the following triangle of equalities commutes:
   \[ \xymatrix{
     G\circ (1_B \circ F) \ar@{=}[rr] \ar@{=}[dr] &&
     (G\circ 1_B)\circ F \ar@{=}[dl] \\
-    & G \circ F}
+    & G \circ F.}
   \]
 \end{lem}