 Here is a simple theory which goes in that direction (Wolniewicz 1982). Let us take the notion of a fact containing another fact as a primitive. We shall use ‘\(x \le y\)’ for ‘\(x\) is contained in \(y\)’, and we shall take relation \(\le\) to be reflexive, antisymmetric and transitive. One option is to define fact containment in modal terms (i.e., define ‘\(x \le y\)’ as ‘necessarily, \(x\) exists if \(y\) does’), but we shall remain neutral on this issue.