cases of_decide_eq_true hb₁
case cons
α : Type u
β : Type v
inst✝ : DecidableEq β
lb : List β
hnodup : Nodup lb
f : α → β
a : α
la : List α
IH : countP (fun b => decide (∃ a, a ∈ la ∧ f a = b)) lb ≤ length la
b₁ b₂ : β
hb₁ : decide (f a = b₁) = true
hb₂ : decide (f a = b₂) = true
⊢ b₁ = b₂
case cons.refl
α : Type u
β : Type v
inst✝ : DecidableEq β
lb : List β
hnodup : Nodup lb
f : α → β
a : α
la : List α
IH : countP (fun b => decide (∃ a, a ∈ la ∧ f a = b)) lb ≤ length la
b₂ : β
hb₂ : decide (f a = b₂) = true
hb₁ : decide (f a = f a) = true
⊢ f a = b₂