The delta structures 200 have {HEAD ~ a lattice} 210 of interconnected strands which intersect to define a plurality of {TAIL ~ cells} 220 
The delta structures 200 have { HEAD ~ a lattice } 210 of interconnected strands which intersect to define a plurality of { TAIL ~ cells } 220
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH