One-parameter groups and combinatorial physics
  In this communication, we consider the normal ordering of sums of elements of the form (a*^r a a*^s), where a* and a are boson creation and annihilation operators. We discuss the integration of the associated one-parameter groups and their combinatorial by-products. In particular, we show how these groups can be realized as groups of substitutions with prefunctions. 
Gerard Duchamp (1), Karol A. Penson (2), Allan I. Solomon (2,3),   Andrej Horzela (4), Pawel Blasiak (2,4) ((1) University o...