-enumerate all of the input commits (U). And each commit we generate
-will be descended from zero or more of these.
-
-Naturally this set varies over time as we generate more commits. We
-write O_pyn for the set of reachable commits at the point where we
-have just generated T_pyn.
-
-We preserve/ensure
- Tip_Pyn >= pendsof( O_pyn, Pyn )
-(Tip_pyn is computed during traversal for the patch p)
-
-We ensure this property by:
- - we do not generate any commits for pyn other than
- during traversal for pyn
- - so at the start of traversal pendsof ( O, pyn) = pendsof (U, pyn)
- - the traversal steps will takes those pends
+enumerate all of the input commits ($\allsrcs$), so the reachable
+commits are originally the input commits and their ancestors.