I need to be explained step by step clearly. Thanks so much:)

1. Prove that each of the following wff is correct Assume that the domain is Z 2. Show the following version of swap over the integers is correct swap (x, y) x-x-y 3. Prove that each of the following wff is correct. Assume that the domain is Z a. true if x!-y then x-y-y b. true if xcy then y-y-1; else x-;y-y (x-y Prove that the following wff is correct where x and y are integers. loop invariant xy and even (x-y) while x!-y do x-x-1 end while ?>.y and even (x-y) and x-y} // post condition 5. Prove the following function for computing n! is corect. function fac (n: nonneg int) the initial condition f positive int i: nonneg int while (i0) do f-fi end while return () You will need to find out the loop invariant first