Left and Right reference stackobjects

consider the problem:

a + a + a = 45
b + b + a = 23
c + b + b = 10
c + b + b * a = ?

The solution:

main > ls
15 	| (/ 45 3)
4 	| (/ (- 23 15) 2)
2 	| (- 10 (* 2 4))
66 	| (+ (* (+ 15 1) 4) 2)

would be nice for to have a Number subclass that takes the value of the previouse or next stack item. This requieres stack awear stackobjects