def infix2prefix(self, lst):
        """
        starting from right the left
        """
        stk = []
        pre = []
        for elt in reversed(lst):
            if elt.isdigit():
                pre.append(elt)
            elif elt == ")":
                stk.append(elt)
            elif elt == "(":
                while stk and stk[-1] != ")":
                    pre.append(stk.pop())
                stk.pop()
            else:
                while stk and self.precedence(stk[-1]) < self.precedence(elt):  # < rather than <=
                    pre.append(stk.pop())
                stk.append(elt)

        while stk:
            pre.append(stk.pop())

        pre.reverse()
        return pre
dataset/ETHPy150Open algorhythms/LintCode/Convert Expression to Polish Notation.py/Solution.infix2prefix/swapped operands of `<`