- more set operations
- more set operations

AlanZatarain/pysal,google-code-export/pysal,Alwnikrotikz/pysal,pombreda/pysal,tectronics/pysal,google-code-export/pysal,AlanZatarain/pysal,pombreda/pysal,google-code-export/pysal,pombreda/pysal,tectronics/pysal,pombreda/pysal,Alwnikrotikz/pysal,tectronics/pysal,Alwnikrotikz/pysal,AlanZatarain/pysal,google-code-export/pysal