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