feat(data/equiv/basic): subtype_equiv_psigma (#9688)
feat(data/equiv/basic): subtype_equiv_psigma (#9688)



- [x] depends on: #9687

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Co-authored-by: Scott Morrison <63f04b4d96235eb042cc46d94f14d241d2a26722@gmail.com>

leanprover-community/mathlib,leanprover-community/mathlib