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Proof step 2 from proof butlast-app (previous step)

⊦ str1 = "", (str0 + str1).butlast = str0 + str1.butlast

User applied rule insert rewrite lemma

And obtained the following new goals

Proof step 3:
⊦ str.butlast = l→s(s→l(str).butlast)
Proof step 4:
⊦ str1 = "", l→s(s→l(str0 + str1).butlast) = str0 + str1.butlast

Rule argument

spec: string-ops inst: name: butlast-def seq: ⊦ str.butlast = l→s(s→l(str).butlast) subst: [str] → [str0 + str1] flags: rewrite, current

Additional information

Used terms: str0 + str1