Theorem: Assignment.addNeg_of_addPos_eq_both (LeanSAT/LRAT/Assignment.lean)

State before:
assignment : Assignment
⊢ assignment.addPosAssignment.addNegAssignment = both
Tactic:
rw [addNegAssignment, addPosAssignment]
State after:
assignment : Assignment
⊢ (match
      match assignment with
      | pos => pos
      | neg => both
      | both => both
      | unassigned => pos with
    | pos => both
    | neg => neg
    | both => both
    | unassigned => neg) =
    both

State before:
assignment : Assignment
⊢ (match
      match assignment with
      | pos => pos
      | neg => both
      | both => both
      | unassigned => pos with
    | pos => both
    | neg => neg
    | both => both
    | unassigned => neg) =
    both
Tactic:
cases assignment <;> simp
State after:
no goals