{TAIL ~ The block} comprises {HEAD ~ a front surface} and a back surface adjoined by first and second side surfaces, a top surface and a bottom surface each lying adjacent the front, back, and first and second side surfaces 
{ TAIL ~ The block } comprises { HEAD ~ a front surface } and a back surface adjoined by first and second side surfaces , a top surface and a bottom surface each lying adjacent the front , back , and first and second side surfaces
TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH