| str.char1 = str0.char1, str.rstring = str0.rstring ⊦ str0 = "", str = "", str = str0 |
⊦ str ≠ "" → (char = str.char1 ∧ str0 = str.rstring ↔ str = char + str0)
str = char + str1, char = str0.char1, str1 = str0.rstring ⊦ str0 = "", str = "", str = str0
Used terms: str, char0, str1