| pos(char1, str0) = pos(char2, str0), pos(char2, str0) < # str0, ∀ char0, char3. pos(char0, str0) = pos(char3, str0) ∧ pos(char3, str0) < # str0 → char0 = char3 ⊦ char2 = char, char1 = char2, char ' + str0 = "", char1 = char, str0 = "" |
Used terms: char1, char2