Atomic Diagram

Given a structure M and a language expanded by a constant for each element of M, the atomic diagram is the set of all atomic and negated atomic sentences in that expanded language that are true in M; it records the complete atomic information about M relative to those constants.

For a structure A, the atomic diagram AtDiag(A) is the subset of the elementary diagram consisting only of the atomic sentences (no negations) in the language expanded by constants c_a naming each element of A that are true in A.