The procedure Decompose_Diff decomposes an expression in a list of elementary components i.e. powers of terms and functions. For example will be decomposed into . This procedure may be used to design a ALIAS_FSIMPLIFY procedure of MakeF so that the elementary components are evaluated only once even if they have multiple occurences in the expression. The list of elementary components may be found in the global variable ALIAS_TERMS. For a list of expression one has to use Decompose_Diff_List that will provide a list sorted by decreased order of length (as defined by the length procedure of Maple.