Sentence:Yet in Judd's [e1]stack[/e1] of galvanized-iron [e2]boxes[/e2], all of the units are identical; they are set on the wall and separated, so that none is subordinated to another's weight (and also so that the space around them plays a role in the work equivalent to theirs); and their regular climb -- each of the twelve boxes is nine inches high, and they rest nine inches apart -- suggests an infinitely extensible series, denying the possibility of a crowning summit.
 e1: stack. 
 e2 : boxes.
Answer: Member-Collection(e2,e1)