exact h insertUnit_success
n : Nat
assignments : Array Assignment
assignments_size : assignments.size = n
units : Array (Literal (PosFin n))
foundContradiction : Bool
l : Literal (PosFin n)
insertUnit_res : Array (Literal (PosFin n)) × Array Assignment × Bool :=
  insertUnit (units, assignments, foundContradiction) l
h : foundContradiction = true → ∃ i, assignments[i.val] = both
l_in_bounds : l.fst.val < assignments.size
hl : hasAssignment l.snd assignments[l.fst.val]! = true
insertUnit_success : (units, assignments, foundContradiction).snd.snd = true
⊢ ∃ j, assignments[j.val] = both
no goals