Chang-Mundici construction of an enveloping unital lattice-group of a BL-algebra

For any BL-algebra L, we construct an associated lattice ordered Abelian group GL that coincides with the Chang’s `-group of an MV-algebra when the BL-algebra is an MValgebra. We prove that the Chang’s group of the MV-center of any BL-algebra L is a direct summand in GL. We also find a direct description of the complement S(L) of the Chang’s group of the MV-center in terms of the filter of dense elements of L. Finally, we compute some examples of the group GL.