A type-4 discount situation is where the mailer reduces the work required by changing his behavior in efficient ways that were either not predicted or that do not seem particularly associated with the nature of the discount.
A type-4 discount involves the mailer decreasing the work required.
and i thought well if i ride my bike the wind chill will be close to zero it will last seven minutes six minutes if i walk it'll be ten degrees warmer but it will last twenty minutes