Two pieces of hearsay I have encountered about Robinson's Q:
- Q fails to satisfy the Löb derivability conditions;
- Pudlák criticised the Löb derivability conditions and suggested rival, weaker conditions.
Which leads to three questions, if the above are right:
- Which derivability condition(s) does Q not satisfy;
- What were Pudlák's rival conditions and what was his complaint with the Löb conditions; and
- Does Q satisfy the rival conditions?
These questions arose from Carl Mummert's answer to a math.sx question of mine, Can Robinson's Q prove Presburger arithmetic consistent?.