 That S5 may be axiomatized both by \(\{\text{K},\text{T},\text{B},\text{4}\}\) and \(\{\text{K},\text{T},\text{5}\}\) may be seen through the frame properties of the axioms: every reflexive and euclidean relation (T and 5) is an equivalence relation (T, B, and 4). This also shows the redundancy of 4: If one has assumed a relation reflexive and euclidean, then it adds nothing new to additionally assume it to be transitive. In general, having an understanding of the interplay between relational properties is of great aid in seeing relationships between modal logics. For example, noticing that every reflexive relation is also serial means that all formulas valid on the class of serial models are also valid on the class of reflexive models. Hence, every theorem of D is thus a theorem of T. Hence T is at least as strong as D (i.e., \(\textbf{D}\subseteq\textbf{T}\)). That T is also strictly stronger (not \(\textbf{T}\subseteq\textbf{D}\)) can be shown by finding a serial, non-reflexive model which does not satisfy some theorem of T (for example \(K_{a}p\rightarrow p\)).