Submission date: 1 January 2016.

Abstract:

We investigate closure operators and describe their properties for E-combinations and P-combinations of structures and their theories. We prove, for E-combinations, that the existence of a minimal generating set of theories is equivalent to the existence of the least generating set, and characterize syntactically and semantically the property of the existence of the least generating set. For the class of linearly ordered language uniform theories we solve the problem of the existence of least generating set with respect to E-combinations and characterize that existence in terms of orders.

Mathematics Subject Classification: 03C30, 03C15, 03C50, 54A05

Keywords and phrases:

Full text arXiv 1601.00043: pdf, ps.