How to link up five cities with highways. . . or to make sure that each of five children in a checker match plays every other one. . . or to cross all seven of the bridges of Konigsberg without crossing any of them twice: these are problems in networks, and Holt explains the principles here with reference to odd and even points and whether given networks are traceable. As for the Konigsberg problem--as Euler, inventor of topography, demonstrated, you can't. A mental trip for young mathematicians, with less busy work and more stimulation than most in the series.