| Article ID: | iaor19912042 |
| Country: | Netherlands |
| Volume: | 31 |
| Issue: | 2 |
| Start Page Number: | 167 |
| End Page Number: | 180 |
| Publication Date: | Apr 1991 |
| Journal: | Discrete Applied Mathematics |
| Authors: | Goodman Jacob E., Pollack Richard |
There are several natural ways to extend the notion of the