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Proof step 2 from proof len-zero (previous step)

# str = 0 ⊦ str = ""

User applied rule structural induction

And closed the goal!

Rule argument

indvar: str

Additional information

Used simplifier rules: Length-rec: ⊦ #(char ' + str) = # str + 1;%string freely generated by "", +;;%chartostring-01: ⊦ char + str = char ' + str; from specification string-append%assoc: ⊦ (str1 + str2) + str3 = str1 + str2 + str3; from specification string-append%z-01: ⊦ m + n = 0 ↔ m = 0 ∧ n = 0; from specification nat-basic2%a: ⊦ (m + n0) + n1 = m + n0 + n1; from specification nat-basic2%c: ⊦ m + n = n + m; from specification nat-basic2