mathlib

38904ac8 - feat(data/fintype/basic): card_eq_zero_equiv_equiv_pempty (#3238)

feat(data/fintype/basic): card_eq_zero_equiv_equiv_pempty (#3238) Adds a constructive equivalence `α ≃ pempty.{v+1}` given `fintype.card α = 0`, which I think wasn't available previously. I would have stated this as an `iff`, but as the right hand side is data is an `equiv` itself. Co-authored-by: Scott Morrison <scott.morrison@gmail.com>