Convergence estimates for some composition operators

There are different methods available in literature to construct a new operator. One of the methods to construct an operator is the composition method. It is known that Baskakov operators can be achieved by composition of Post Widder $P_n$ and Sz\'asz-Mirakjan $S_n$ operators in that order, which is a discretely defined operator. But when we consider different order composition namely $S_n\circ P_n$, we get another different operator. Here we study such and we establish some convergence estimates for the composition operators $S_n\circ P_n$, along with difference with other operators. Finally we found the difference between two compositions by considering numeric values.