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