stack 0
stack 1
stack 2
buffer 0
buffer 1
buffer 2
stack 0,child 0
stack 0,child 1
stack 0,child -2
stack 0,child -1
stack 1,child 0
stack 1,child 1
stack 1,child -2
stack 1,child -1
stack 0,child 0,child 0
stack 0,child -1,child -1
stack 1,child 0,child 0
stack 1,child -1,child -1