/**
* Returns whether this function always evaluates to the same numerical value, i.e. it is of the
* form f(x1,...,xn) = c.
*
* @return true iff constant
*/
public final boolean isConstantFunction() {
if (isConstantFunction) return true;
for (int i = 0; i < fVars.length; i++) if (expression.contains(fVars[i])) return false;
return true; // none of the vars appears in the expression
}
