7.8.x. Exercise questions
Use the system of derivations to find structures dividing premises from conclusions in the cases below. You will need to use the rule UG+.
| 1. | ∀x ¬ ∀y ¬ Rxy / ∀x ¬ Rxx |
| 2. | ∀x ¬ ∀y Rxy / ¬ ∀x Rxa |
| 3. | ∀x ¬ ∀y Rxy / ∀x ¬ Rax |
The exercise machine doesn’t incorporate the rule UG+, so derivations for arguments where it is needed will never end.