00271nam a2200109 a 450000500170000008200130001710000130003024500320004326000520007530000220012770000120014920251203110444.0  a516bBIR  aBirkhoff  aBasic geometrybanswer book  aProvidencebAmerican Mathematical Societyc1963  a[96]p.c22cm.bPB  aBeatley