8 lines
217 B
Text
8 lines
217 B
Text
axiom I : Type
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definition F (X : Type) : Type := (X → Prop) → Prop
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axiom unfoldd : I → F I
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axiom foldd : F I → I
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axiom iso1 : ∀x, foldd (unfoldd x) = x
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theorem iso2 : ∀x, foldd (unfoldd x) = x
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:= sorry
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