rw [removeNegAssignment, addNegAssignment]
assignment : Assignment
h : ¬assignment.hasNegAssignment = true
⊢ assignment.addNegAssignment.removeNegAssignment = assignment
assignment : Assignment
h : ¬assignment.hasNegAssignment = true
⊢ (match
      match assignment with
      | pos => both
      | neg => neg
      | both => both
      | unassigned => neg with
    | pos => pos
    | neg => unassigned
    | both => pos
    | unassigned => unassigned) =
    assignment