Multiply by the rule

You will add and multiply complex numbers by the rules alone, each number given by its two real parts. Then the checker compares your answers with Python's own complex numbers.

The idea. $(a + ib) + (c + id) = (a + c) + i(b + d)$, and $(a + ib)(c + id) = (ac - bd) + i(ad + bc)$.

Your tasks.

1. Finish add(a, b, c, d): return the real part and the imaginary part of the sum, as a pair.
2. Finish mul(a, b, c, d) in the same way for the product.
3. Use mul to set square to the pair for $(2 + 5i)^2$.