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