return new StmtAssign(stmt.getContext(), lhs, new_rhs);
return new StmtAssign(stmt.getContext(), lhs, new_rhs, stmt.getOp());
    public Object visitStmtAssign(StmtAssign stmt)    {	Expression lhs = stmt.getLHS();        Expression rhs = stmt.getRHS();	Expression new_rhs = (Expression)stmt.getRHS().accept(this);	if (!new_rhs.equals(rhs)) {	    return new StmtAssign(stmt.getContext(), lhs, new_rhs);	} else {	    return stmt;	}    }