A linear coloring of a graph G is a proper vertex coloring such that the graph induced by the vertices of any two color classes is the union of vertex-disjoint
In this paper we introduce a class of right S-acts called retractable S-acts which are right S-acts with homomorphisms into their all subacts. We also give some
First,we give a module estimation of the singular integral with a differential element.Then by proving the existences of Cauchy principal value we obtain the tr