The BGL (Boost Graph Library) defines tie(), which is exactly what the tie() defined in STLExtras.h. The header files of GBL use boost::tie(), and other boost libraries use boost::tie() too. How to resolve the ambiguity for compiler? -- Tzu-Chien Chiu, 3D Graphics Hardware Architect <URL:http://www.csie.nctu.edu.tw/~jwchiu>