<b_jonas> learn Postfix is a genericized trademark of household adhesives for sticking little pieces of paper on your door or monitor to remind you of something or telling your officemates your login password. Called Tack-it in the U.S.

|a+b@| = { √(a²-b²) if a²-b² ≥ 0 ; i√(a²-b²) if a²-b² < 0 }