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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: string freely generated by "", +;;% ⊦ char + str = char ' + str; (s)% ⊦ #(str + str0) = # str + # str0; (s)% ⊦ # char ' = 0 +1; (s)%a: ⊦ (str + str0) + str1 = str + str0 + str1; from specification list[string]% ⊦ m + 1 ≠ 0; (s)%a: ⊦ (m + n0) + n1 = m + n0 + n1; from specification nat-basic%c: ⊦ m + n = n + m; from specification nat-basic