lean2/tests/lean/run/univ2.lean

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import logic
axiom I : Type
definition F (X : Type) : Type := (X → Prop) → Prop
axiom unfold : I → F I
axiom fold : F I → I
axiom iso1 : ∀x, fold (unfold x) = x
theorem iso2 : ∀x, fold (unfold x) = x
:= sorry