return null ;
// Corner case: sameTerm is false for string/plain literal,
// but true in the graph for graphs with
ExprFunction2 eq = (ExprFunction2)e ;
Expr left = eq.getArg1() ;
Expr right = eq.getArg2() ;
Var var = null ;
NodeValue constant = null ;
if ( left.isVariable() && right.isConstant() )