α : Type u_2
β : α → Type u_1
f : ((a : α) → Part (β a)) → (a : α) → Part (β a)
x : α
h' : ¬∃ i, (Fix.approx f i x).Dom
⊢ (assert (∃ i, (Fix.approx f i x).Dom) fun h =>
      WellFounded.fix (_ : WellFounded (Upto.GT fun x_1 => (Fix.approx f x_1 x).Dom)) (fixAux f) Upto.zero x) =
    none
α : Type u_2
β : α → Type u_1
f : ((a : α) → Part (β a)) → (a : α) → Part (β a)
x : α
h' : ¬∃ i, (Fix.approx f i x).Dom
⊢ Part.fix f x = none
dsimp [Part.fix]
no goals
α : Type u_2
β : α → Type u_1
f : ((a : α) → Part (β a)) → (a : α) → Part (β a)
x : α
h' : ¬∃ i, (Fix.approx f i x).Dom
⊢ (assert (∃ i, (Fix.approx f i x).Dom) fun h =>
      WellFounded.fix (_ : WellFounded (Upto.GT fun x_1 => (Fix.approx f x_1 x).Dom)) (fixAux f) Upto.zero x) =
    none
rw [assert_neg h']