rw [colImpliesName_eq_2, lookup_eq_2]
η : Type u_η
dec_η : DecidableEq η
schema : Schema
nm : η
τ : Type u_1
head✝ : Header
ss : List Header
h : HasCol (nm, τ) ss
⊢ lookup (head✝ :: ss) { fst := nm, snd := colImpliesName (HasCol.tl h) } = (nm, τ)
η : Type u_η
dec_η : DecidableEq η
schema : Schema
nm : η
τ : Type u_1
head✝ : Header
ss : List Header
h : HasCol (nm, τ) ss
⊢ lookup ss { fst := nm, snd := colImpliesName h } = (nm, τ)