In use, the blocks may be stacked to provide an interlocking structure wherein the protrusions of {HEAD ~ one block interfit} within {TAIL ~ the insets} of another block 
within
In use , the blocks may be stacked to provide an interlocking structure wherein the protrusions of { HEAD ~ one block interfit } within { TAIL ~ the insets } of another block
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH