simp only [removeNegAssignment, hasNegAssignment, Bool.not_eq_true]
assignment : Assignment
⊢ ¬assignment.removeNegAssignment.hasNegAssignment = true
assignment : Assignment
⊢ (match
      match assignment with
      | pos => pos
      | neg => unassigned
      | both => pos
      | unassigned => unassigned with
    | pos => false
    | neg => true
    | both => true
    | unassigned => false) =
    false