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when toggle format what by license comment
Jul 6, 2022 at 11:13 history edited Martin Sleziak CC BY-SA 4.0
http -> https (the question was bumped anyway)
Aug 17, 2010 at 3:23 comment added Alfonso Gracia-Saz The 15 puzzle is a good way of introducing groupoids.
Aug 14, 2010 at 21:55 history answered Somnath Basu CC BY-SA 2.5