{TAIL ~ Preferably one grid field} of the second grid structure fits onto several grid fields of {HEAD ~ the first grid structure} 
{ TAIL ~ Preferably one grid field } of the second grid structure fits onto several grid fields of { HEAD ~ the first grid structure }
TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD