Countable structures of given age
Dugald Macpherson, Maurice Pouzet, Robert E. Woodrow · Journal of Symbolic Logic · 1992
Abstract Let L be a finite relational language. The age of a structure over L is the set of isomorphism types of finite substructures of . We classify those ages for which there are less than 2ω countably infinite pairwise nonisomorphic L-structures of age .