Some comparison results on equivalence groups
  This paper deals with the comparison of two common types of equivalence groups of differential equations, and this gives rise to a number of results presented in the form of theorems. It is shown in particular that one type can be identified with a subgroup of the other type. Consequences of this comparison related in particular to the determination of invariant functions of the differential equations are also discussed. 
J. C. Ndogmo
math.DG