GENERAL
C >= D C is descendant of D, partial order
- C \haspatch D C contains changes from D, partial order
+ D \isin C C contains changes from D, partial order
Patch P has two sets P+, P-
Ancestors A(C,P) = { Ca \elem C | Ca \elem P }
Ends E(C,P) = maximal elements of A(C,P)