if the following are true:

• index of value value in tree = i
• the element at index i of stack tree = node (value, (-1), right)
• the element at index right of stack tree = node (rvalue, rleft, rright)
• find parent index of tree = p
• the element at index p of stack tree = node (pval, i, pright)

then pop value from tree tree = result of storing (node (value, (-1), (-1))) at index i of stack (result of storing (node (pval, right, pright)) at index p of stack tree)