Type specimens are the cornerstones of modern taxonomy and systematics, should be starting point any study diversity, especially considering increasing ability to sample them genetically. However, no compilation type material (beyond holotypes) exists for turtles (Order Testudines). This is first attempt locate compile a list all (holotypes, paratypes, syntypes, lectotypes, neotypes, etc.) desc...

We investigate several variants of the homomorphism problem: given two relational structures, is there a homomorphism from one to the other? The input structures are possibly infinite, but definable by first-order interpretations in a fixed structure. Their signatures can be either finite or infinite but definable. The homomorphisms can be either arbitrary, or definable with parameters, or defi...