def exp(b, c):
    """Returns: b**c
    Precondition: b a float, c ≥ 0 an int"""
    assert type(b) == float, repr(b) + " is not a float "
    assert c >= 0 and type(c) == int, repr(c) + 'is the wrong format'
    if c == 0:
        return 1
    left = b
    right = exp(b, c-1)

    return left * right