absurd (Fin.find?_none j h)
n : Nat
s : Setoid (Fin n)
inst✝ : DecidableRel Setoid.r
i j : Fin n
hij : Setoid.r i j
i' : Fin n
hi' : (Fin.find? fun b => decide (Setoid.r i b)) = some i'
h : (Fin.find? fun b => decide (Setoid.r j b)) = none
⊢ (let_fun this := ⋯;
    encodeSubtype (repr s) ⟨i', this⟩) =
    absurd ⋯ ⋯
n : Nat
s : Setoid (Fin n)
inst✝ : DecidableRel Setoid.r
i j : Fin n
hij : Setoid.r i j
i' : Fin n
hi' : (Fin.find? fun b => decide (Setoid.r i b)) = some i'
h : (Fin.find? fun b => decide (Setoid.r j b)) = none
⊢ ¬decide (Setoid.r j j) = false