 Next, propositions \(M, N, O, \ldots\) are said to be deducible from propositions \(A, B, C, \ldots\) with respect to variable ideas \(i, j, k, \ldots\) iff \(A, B, C, \ldots, M, N, O, \ldots\) are compatible with respect to variable ideas \(i, j, k, \ldots\) and the idea [verifying ideas for \(A, B, C, \ldots\) relative to \(i, j, k, \ldots\)] is included in the idea [verifying ideas for \(M, N, O, \ldots\) relative to \(i, j, k, \ldots\)] in the previously defined sense, i.e., iff the extension of the former is a subset of the extension of the latter (TS, § 155). 