apply and_congr_right'
case cons
α : Type u
inst✝ : DecidableEq α
a b : α
x : Array α
IH : Nodup (push x a) ↔ Nodup x ∧ ¬a ∈ x
⊢ ¬b ∈ x ∧ ¬b = a ∧ Nodup x ∧ ¬a ∈ x ↔ ¬b ∈ x ∧ Nodup x ∧ ¬a = b ∧ ¬a ∈ x
case cons.h
α : Type u
inst✝ : DecidableEq α
a b : α
x : Array α
IH : Nodup (push x a) ↔ Nodup x ∧ ¬a ∈ x
⊢ ¬b = a ∧ Nodup x ∧ ¬a ∈ x ↔ Nodup x ∧ ¬a = b ∧ ¬a ∈ x