#
# Lab 4b, Task 2
#

def bitwise_or(b1, b2):
    """ computes and returns the bitwise OR of binary numbers b1 and b2
        inputs: b1 and b2 are strings that represent binary numbers
    """
    if b1 == '' and b2 == '':
        return ''
    elif b1 == '':
        return b2
    elif b2 == '':
        return b1
    else:
        or_rest = bitwise_or(b1[:-1], b2[:-1])
        if b1[-1] == '1' or b2[-1] == '1':
            return or_rest + '1'
        else:
            return or_rest + '0'