Character Compatibility
| A | B | |
| T1 | 1 | 1 |
| T2 | 1 | 0 |
| T3 | 0 | 1 |
| T4 | 0 | 0 |
| • | Two characters A, B are compatible if there do not exits four taxa containing all four combinations as in the table | |
| • | Fact: there exits perfect phylogeny if and only if and only if all pairs of characters are compatible |
