FORMULAS
| ➀ | forall s, t, u (s ->* t & s ->* u => t join u) |
| ➁ | forall s, t, u (s ->* t & s -> u => t join u) |
| ➂ | forall t, u (t <->* u => t join u) |

| ➀ | forall s, t, u (s ->* t & s ->* u => t join u) |
| ➁ | forall s, t, u (s ->* t & s -> u => t join u) |
| ➂ | forall t, u (t <->* u => t join u) |