0! = 1
1! = 1
1 * 1 = 1
1 + 0 = 1
1^n = 1 for any n, even complex
n/n = 1 for any n, even complex, except for 0.
n^0 = 1 for any n, even complex, except for 0.
-e^(pi*i) = 1
sqrt(sqrt(sqrt.... ( n ) ... ) ) = 1 for any n, even complex ones, except for 0