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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
from typing import List


def string_xor(a: str, b: str) -> str:
    """ Input are two strings a and b consisting only of 1s and 0s. Perform binary XOR on these inputs and return result also as a string. '100' """
    def xor(i, j):
        if i == j:
            return '0'
        else:
            return '1'

    return ''.join(xor(x, y) for x, y in zip(a, b))
