It returns X[Y] into output box when you put "X Y" in input box.
w 3
w+5 3
(0,0,(0,0,w+5)) 3
(0,0,(0,0,w+w+2)) 3
(0,0,W) 3
(0,0,(0,1,W)) 3
(0,0,(0,W,0)) 3
(0,0,(W,0,0)) 3
↓
3
w+1+1+1+1
(0,0,(0,0,w+1+1+1+1)+(0,0,w+1+1+1+1)+(0,0,w+1+1+1+1))
(0,0,(0,0,w+w+1)+(0,0,w+w+1)+(0,0,w+w+1))
(0,0,(0,0,(0,0,w)))
(0,0,(0,1,(0,0,(0,1,(0,0,(0,1,(0,0,(0,1,1))))))))
(0,0,(0,(0,0,(0,(0,0,(0,e,0)),0)),0))
(0,0,((0,0,((0,0,((0,0,(1,0,0)),0,0)),0,0)),0,0))