(==) (Add (Neg (Opd 5)) (Sub (Opd 7) (Opd 3))) (Add (Neg (Opd 5)) (Sub (Opd 7) (Opd 3))) == True
(==) (Add (Neg (Opd 5)) (Sub (Opd 7) (Opd 3))) (Add (Neg (Opd 5)) (Opd 4)) == True

(<) (Sub (Opd 7) (Opd 3)) (Add (Neg (Opd 5)) (Sub (Opd 7) (Opd 3))) == True
(<) (Add (Neg (Opd 5)) (Sub (Opd 7) (Opd 3))) (Add (Neg (Opd 5)) (Opd 4)) == False

(<=) (Sub (Opd 7) (Opd 3)) (Add (Neg (Opd 5)) (Sub (Opd 7) (Opd 3))) == True
(<=) (Add (Neg (Opd 5)) (Sub (Opd 7) (Opd 3))) (Add (Neg (Opd 5)) (Opd 4)) == True

eval (VSub (VCar 'a') (VAdd (VOpd 17) (VOpd 4))) == (VSub (VCar 'a') (VOpd 21))
eval (VSub (VCar 'a') (VAdd (VVar 'b') (VOpd 4))) == (VSub (VCar 'a') (VAdd (VVar 'b') (VOpd 4)))

evalInState (VSub (VCar 'a') (VAdd (VOpd 17) (VOpd 4))) (State [('a',30),('b',2),('a',5)]) == (VOpd 9)
evalInState (VSub (VCar 'a') (VAdd (VVar 'b') (VOpd 4))) (State [('b',2)]) == (VSub (VCar 'a') (VOpd 6))

(==) (VSub (VCar 'a') (VAdd (VOpd 17) (VOpd 4))) (VSub (VCar 'b') (VAdd (VOpd 17) (VOpd 4))) == True
(==) (VSub (VCar 'a') (VAdd (VOpd 4) (VOpd 17))) (VSub (VCar 'a') (VAdd (VOpd 17) (VOpd 4))) == False