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Stars indicate particularly interesting answers or good places
to begin browsing. Selected answers to common questions: Four-
color map theorem. How many handshakes? Squares in a
checkerboard. - Graph Theory [09/29/2001] Why is a graph with
five vertices, each having a degree of 3, impossible? - Graph
Without Crossing Lines [7/19/1996] There are three houses and
three utilities: how do you connect each of the houses
individually to the three utilities without crossing your -
Greatest Integer Functions [09/27/1998] Can you help me solve
for the graph of [y]=[x], where  is the greatest - How Many are
in the Group? [10/17/1996] Everyone in the group had been to at
least one of the parks... - How Many Balls Would Be Used?
[5/8/1995] Consider a knock-out tournament, say tennis or ping-
pong, with n participants. The winner of any game goes on to the
next round and the loser retires...How many balls have been used
in the tournament? - How Many Distinct Patte