intro j hj
case cons
t : Prop
l : List Prop
ih : ∀ {j : Nat} (hj : j < l.length), (orN (l.eraseIdx j) ∨ l[j]) = orN l
⊢ ∀ {j : Nat} (hj : j < (t :: l).length), (orN ((t :: l).eraseIdx j) ∨ (t :: l)[j]) = orN (t :: l)
case cons
t : Prop
l : List Prop
ih : ∀ {j : Nat} (hj : j < l.length), (orN (l.eraseIdx j) ∨ l[j]) = orN l
j : Nat
hj : j < (t :: l).length
⊢ (orN ((t :: l).eraseIdx j) ∨ (t :: l)[j]) = orN (t :: l)