simp only [flatten, header, Schema.names]
η : Type u_η
dec_η : DecidableEq η
sch : Schema
t : Table sch
cs : ActionList Schema.flattenList sch
⊢ header (flatten t cs) = header t
η : Type u_η
dec_η : DecidableEq η
sch : Schema
t : Table sch
cs : ActionList Schema.flattenList sch
⊢ List.map Prod.fst (Schema.flattenLists sch cs) = List.map Prod.fst sch