# There is some source file with TODO labels inside


def sum(a, b):
    # TODO(slukjanov): implement how to add numbers
    return None

def sum(a, b):
    # TODO(slukjanov): implement how to subtract numbers
    return None

def divide(a, b):
    # TODO(aignatov): implement how to divide numbers
    return None

def mul(a, b):
    # TODO(mimccune): implement how to multiply numbers
    return None
