intro insertUnit_res l' l'_in_insertUnit_res
n : Nat
units : Array (Literal (PosFin n))
assignments : Array Assignment
foundContradiction : Bool
l : Literal (PosFin n)
⊢ let insertUnit_res := insertUnit (units, assignments, foundContradiction) l;
  ∀ (l' : Literal (PosFin n)), l' ∈ insertUnit_res.fst.data → l' = l ∨ l' ∈ units.data
n : Nat
units : Array (Literal (PosFin n))
assignments : Array Assignment
foundContradiction : Bool
l : Literal (PosFin n)
insertUnit_res : Array (Literal (PosFin n)) × Array Assignment × Bool :=
  insertUnit (units, assignments, foundContradiction) l
l' : Literal (PosFin n)
l'_in_insertUnit_res : l' ∈ insertUnit_res.fst.data
⊢ l' = l ∨ l' ∈ units.data