if (!existingVariable.equals(variable))
if (!existingVariable.sameAs(variable)) { if (DEBUG) System.out.println("\tConflicting variable " + varName);
	protected static BindingSet addOrCheckDefinition(String varName, Variable variable, BindingSet bindingSet) {		Variable existingVariable = lookup(varName, bindingSet);		if (existingVariable == null) {			bindingSet = new BindingSet(new Binding(varName, existingVariable), bindingSet);		} else {			if (!existingVariable.equals(variable))				return null;		}		return bindingSet;	}