exact Fin.find?_some j hj
case a
n : Nat
s : Setoid (Fin n)
inst✝ : DecidableRel Setoid.r
k : Fin (quot s)
i : Fin n
h✝ : (Quotient.mk s i).liftOn (Fin.getRepr s) ⋯ = k
j : Fin n
hj : (Fin.find? fun b => decide (Setoid.r i b)) = some j
h : decodeSubtype (repr s) k = ⟨j, ⋯⟩
⊢ decide (i ≈ ⟨j, ⋯⟩.val) = true
no goals