◎◎◎ rubble ⪢⪢
http://qindex.info/i.php?x=12526

○○○ topology ⪢⪢
Topology is a branch of math, which is kind of like geometry. It studies shapes and spaces, but ones that are arbitrarily stretchy and bendy. It's sometimes called rubber sheet geometry.
http://qindex.info/i.php?x=14104

○○○ rubble ⪢⪢
http://qindex.info/i.php?x=19004

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