Given A = {1, 2, 3, 4} and B = {a, b, c, d}.

We need to define bijections f₁, f₂, f₃ and f₄ from A to B.

Consider f₁ = {(1, a), (2, b), (3, c), (4, d)}

(1) f₁ is one-one because no two elements of the domain are mapped to the same element.

f₁ is also onto because each element in the co-domain has a pre-image in the domain.

Thus, f₁ is a bijection from A to B.

We have f₁^-1 = {(a, 1), (b, 2), (c, 3), (d, 4)}

Using similar explanation, we also have the following bijections defined from A to B -

(2) f₂ = {(1, b), (2, c), (3, d), (4, a)}

We have f₂^-1 = {(b, 1), (c, 2), (d, 3), (a, 4)}

(3) f₃ = {(1, c), (2, d), (3, a), (4, b)}

We have f₃^-1 = {(c, 1), (d, 2), (a, 3), (b, 4)}

(4) f₄ = {(1, d), (2, a), (3, b), (4, c)}

We have f₄^-1 = {(d, 1), (a, 2), (b, 3), (c, 4)}