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