def test_nf():
f = Xor(a, b, c)
g = a * b + a * c + b * c
assert str(f.to_dnf()) == "a' * b' * c + a' * b * c' + a * b' * c' + a * b * c"
assert str(f.to_cnf()) == "(a + b + c) * (a + b' + c') * (a' + b + c') * (a' + b' + c)"
assert str(g.to_cdnf()) == "a' * b * c + a * b' * c + a * b * c' + a * b * c"
assert str(g.to_ccnf()) == "(a + b + c) * (a + b + c') * (a + b' + c) * (a' + b + c)"
