A cover set is a minimal set of attack types necessary to hit a set of typings for some level of damage. For the complete set of typings, there are nine cover sets, each of size ten. If a typing vulnerable only to one attack type is present in the targeted population, that attack type must be part of any coverset. If pure Normal is allowed, Fighting must be present in the cover set. Likewise, pure Electric necessitates Ground, etc. These sets are at the effective damage level.