fac = (lambda self_fix : self_fix(self_fix)) (lambda f: (lambda x : 1 if x == 0 else x * f(f)(x - 1)))

assert fac(1) == 1
assert fac(2) == 2
assert fac(3) == 6
assert fac(4) == 24
assert fac(5) == 120
assert fac(6) == 720
assert fac(7) == 5040
assert fac(8) == 40320
assert fac(9) == 362800
assert fac(10) == 3628000