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Proof step 4 from proof del-size-02 (previous step)

b ∈ s, a ∈ s ⊦ # s = 0, s = ∅, a = b, #(s -- b -- a) = # s - 1 - 1

Heuristic weak cut applied rule cut formula

And closed the goal!

Rule argument

fma: a ∈ s -- b

Additional information

Used simplifier rules: del-size: ⊦ a ∈ s → #(s -- a) = # s - 1;%del-in: ⊦ ¬ a ∈ s → s -- a = s;%del-size: ⊦ a ∈ s → #(s -- a) = # s - 1;%del-in-01: ⊦ a ≠ b → (¬ a ∈ s -- b ↔ ¬ a ∈ s); Used formulas: a ∈ s -- b