Complex Arithmetic
Here are the rules :
x + (a + j b) == (a + x) + j b
(a + j b) + (c + j d) == (a + c) + j (b + d)
x * (a + j b) == (x * a) + j (x * d)
(a + j b) * (c + j d) == (a c - b d) + j (a d + c b)