code: public static Double unaryPreMultiply(PageContext pc, Collection.Key[] keys, double value) throws PageException {
  	VariableReference ref = VariableInterpreter.getVariableReference(pc, keys, true);
  	double rtn = Caster.toDoubleValue(ref.get(pc)) * value;
  	ref.set(rtn);
  	return rtn;
      }
docs: pre multiply