Thisbookwaswrittenfortheactivereader.Thefirstpartconsistsofproblems，frequentlyprecededbydefinitionsandmotivation，andsome-timesfollowedbycorollariesandhistoricalremarks.Mostoftheproblemsarestatementstobeproved，butsomearequestions(isit?，whatis?)，andsomearechallenges(construct，determine).Thesecondpart，averyshortone，consistsofhints.Ahintisaword，oraparagraph，usuallyintendedtohelpthereaderfindasolution.Thehintitselfisnotnecessarilyacon-densedsolutionoftheproblem;itmayjustpointtowhatIregardastheheartofthematter.Sometimesaproblemcontainsatrap，andthehintmayservetochidethereaderforrushingintoorecklessly.Thethirdpart，thelongest，consistsofsolutions：proofs，answers，orconstructions，dependingonthenatureoftheproblem