Let (W,S) be a Coxeter system and H the associated Hecke algebra with unequal parameters. The Laurent polynomials Ms y,w and py,w for y, w ∈ W and s ∈ S play an important role in the representations of H. We study the properties of Ms y,w and py,w, the relations among them, as well as with the left, right and two-sided cells of W . In his book [5], Lusztig gave a systematic introduction to the ...