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Proof step 2 from proof eqpos (previous step)

pos(char1, str) = pos(char2, str), pos(char2, str) < # str ⊦ char1 = char2, str = ""

User applied rule structural induction

And obtained the following new goals

Proof step 3:
∀ char1, char2. pos(char1, str0) = pos(char2, str0) ∧ pos(char2, str0) < # str0 → char1 = char2 ∨ str0 = "", pos(char1, char + str0) = pos(char2, char + str0), pos(char2, char + str0) < #(char + str0) ⊦ char1 = char2, char + str0 = ""

Rule argument

indvar: str

Additional information

Used simplifier rules: string freely generated by "", +;;