For simplicity we follow the rules: x, y, y1, y2, z, a will be arbitrary, f , g, h, h′, f1, f2 will denote functions, i will denote a natural number, X, Y , Z, V1, V2 will denote sets, P will denote a permutation of X, D, D1, D2, D3 will denote non-empty sets, d1 will denote an element of D1, d2 will denote an element of D2, and d3 will denote an element of D3. We now state a number of proposit...