simp only [Bool.not_eq_true] at hb
case neg
assignment : Assignment
b : Bool
hb : ¬b = true
⊢ hasAssignment b (removeAssignment (!b) assignment) = true → hasAssignment b assignment = true
case neg
assignment : Assignment
b : Bool
hb : b = false
⊢ hasAssignment b (removeAssignment (!b) assignment) = true → hasAssignment b assignment = true