| pos(char, sortedchars) = pos(char2, sortedchars) ⊦ char = char2 |
⊦ pos(char1, str) < # str → (pos(char1, str) = pos(char2, str) ↔ char1 = char2)
pos(char, sortedchars) = pos(char2, sortedchars) ⊦ char = char2, pos(char, sortedchars) < # sortedchars
Used terms: char2, sortedchars, char