Darcs.Patch.CommuteFn
type CommuteFn p1 p2
commuterIdFL
commuterFLId
commuterIdRL
commuterRLId
type MergeFn p1 p2
mergerIdFL
type TotalCommuteFn p1 p2
totalCommuterIdFL
totalCommuterFLId
totalCommuterFLFL