Removed obsolete axiom from the defn of Ex(M).

docs/constructions.tex

@@ -163,8 +163,6 @@ The step-indexed equivalence is inductively defined as follows:
 \begin{mathpar}
   \infer{x \nequiv{n} y}{\exinj(x) \nequiv{n} \exinj(y)}
 
-  \axiom{\munit \nequiv{n} \munit}
-
   \axiom{\bot \nequiv{n} \bot}
 \end{mathpar}
 $\exm(-)$ is a locally non-expansive functor from $\COFEs$ to $\CMRAs$.