add cell operator

src/math/mathop.pysty

@@ -127,6 +127,7 @@ __END_OPTIONS_X__
 \def\twedge{\vee} % Semantically correct macros for wedge product
 \def\tsmash{\wedge} % Semantically correct macro for smash product
 \DeclareSimpleMathOperator{sing}
+\DeclareSimpleMathOperator{cell}
 
 %Category Theory
 \DeclareSimpleMathOperator{Ob}