. have h := not_hasPos_of_removePos assignment
  simp [hb, h, removeAssignment, hasAssignment]
case pos
assignment : Assignment
b : Bool
hb : b = true
⊢ ¬hasAssignment b (removeAssignment b assignment) = true

case neg
assignment : Assignment
b : Bool
hb : ¬b = true
⊢ ¬hasAssignment b (removeAssignment b assignment) = true
case neg
assignment : Assignment
b : Bool
hb : ¬b = true
⊢ ¬hasAssignment b (removeAssignment b assignment) = true