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This patch finally (I hope) nails the question of whether (forall a. ty) and (forall a -> ty) are `eqType`: they aren't! There is a long discussion in #22762, plus useful Notes: * Note [ForAllTy and type equality] in GHC.Core.TyCo.Compare * Note [Comparing visiblities] in GHC.Core.TyCo.Compare * Note [ForAllCo] in GHC.Core.TyCo.Rep It also establishes a helpful new invariant for ForAllCo, and ForAllTy, when the bound variable is a CoVar:in that case the visibility must be coreTyLamForAllTyFlag. All this is well documented in revised Notes.
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