All or most pieces of a modern jigsaw puzzle interlock by means of
rounded tabs (interjambs) and indentations (called "blanks") on adjacent
sides. The pieces are normally four-sided and may be uniform in
appearance except for the edges and corners. Some puzzles are termed
"fully interlocking", which means that a group of assembled pieces fit
together tightly enough to be moved without falling apart; sometimes the
connection is tight enough that a solved section will remain attached
when lifted by one piece. Uniformly shaped fully interlocking puzzles,
sometimes called "Japanese Style", are more difficult because pieces are
hard to tell apart.
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