Each substrate has {TAIL ~ a first edge} and {HEAD ~ a second edge} orthogonal with the first edge 
Each substrate has { TAIL ~ a first edge } and { HEAD ~ a second edge } orthogonal with the first edge
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH