| str1.last ∈ str, ∀ char. char ∈ str1 → char ∈ str, ∀ str0, str, str2. # str2 < # str1 → (∀ char. char ∈ str2 → char ∈ str) → string-right-trim(str, str0 + str2) = string-right-trim(str, str0) ⊦ ∀ char. char ∈ str1.butlast → char ∈ str, string-right-trim(str, str0 + str1.butlast) = string-right-trim(str, str0), str0 + str1 = "", str1 = "" |
str1.last ∈ str, char0 ∈ str1.butlast, ∀ char. char ∈ str1 → char ∈ str, ∀ str0, str, str2. # str2 < # str1 → (∀ char. char ∈ str2 → char ∈ str) → string-right-trim(str, str0 + str2) = string-right-trim(str, str0) ⊦ str1 = "", str0 + str1 = "", string-right-trim(str, str0 + str1.butlast) = string-right-trim(str, str0), char0 ∈ str