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Proof step 12 from proof del-04 (previous step)

¬ a ∈ x, perm(y, x), ∀ a. a ∈ x ∨ a ∈ y → #oc(a, x) = #oc(a, y), a ∈ x -1l a ∨ a ∈ y -1l a ⊦ #oc(a, x -1l a) = #oc(a, y -1l a)

Heuristic simplifier applied rule simplifier

And obtained the following new goals

Proof step 13:
perm(y, x), a ∈ y -1l a, a ∈ y, ∀ a. a ∈ x ∨ a ∈ y → #oc(a, x) = #oc(a, y) ⊦ a ∈ x

Rule argument

Additional information

Used simplifier rules: notin: ⊦ ¬ a ∈ x → #oc(a, x) = 0;%oc-zero: ⊦ #oc(a, x) = 0 ↔ ¬ a ∈ x;%in-01-01: ⊦ a ∈ x -1l b → a ∈ x; (forward) from specification list-del%in-02-01: ⊦ ¬ a ∈ x → x -1l a = x; from specification list-del