  With the aim of developing the concepts of positive logic and in response to
a question that was asked by Poizat in one of his articles, I wrote this
article. The main topic is the study of compactness in the extension as a
compact structure. they are based on a fundamental characterization of the
compactness, which was given by Itai Ben Yacov and Poizat in section Basis of
positive logic.
