Because completion operates bottom-up, it follows that Type 5 rules apply before Type 4 rules.
when adjoining an auxiliary tree β 1 to a node η o , the Type 5 completor rules, unifying the bottom feature structure of the foot node of β 1 with the bottom feature structure of the node η o , occurs before the Type 4 completor rules, which reassign the bottom reference variable of η o to the bottom feature structure of the root of β 1 .