| 1: | a__first(0,X) | → nil | |
| 2: | a__first(s(X),cons(Y,Z)) | → cons(mark(Y),first(X,Z)) | |
| 3: | a__from(X) | → cons(mark(X),from(s(X))) | |
| 4: | mark(first(X1,X2)) | → a__first(mark(X1),mark(X2)) | |
| 5: | mark(from(X)) | → a__from(mark(X)) | |
| 6: | mark(0) | → 0 | |
| 7: | mark(nil) | → nil | |
| 8: | mark(s(X)) | → s(mark(X)) | |
| 9: | mark(cons(X1,X2)) | → cons(mark(X1),X2) | |
| 10: | a__first(X1,X2) | → first(X1,X2) | |
| 11: | a__from(X) | → from(X) | |
| 12: | A__FIRST(s(X),cons(Y,Z)) | → MARK(Y) | |
| 13: | A__FROM(X) | → MARK(X) | |
| 14: | MARK(first(X1,X2)) | → A__FIRST(mark(X1),mark(X2)) | |
| 15: | MARK(first(X1,X2)) | → MARK(X1) | |
| 16: | MARK(first(X1,X2)) | → MARK(X2) | |
| 17: | MARK(from(X)) | → A__FROM(mark(X)) | |
| 18: | MARK(from(X)) | → MARK(X) | |
| 19: | MARK(s(X)) | → MARK(X) | |
| 20: | MARK(cons(X1,X2)) | → MARK(X1) | |