Let  be hyperexponential functions of x over a field K of characteristic 0. The AreSimilar(H1,H2,x) command returns true if  and  are similar. Otherwise, it returns false.

H1 and H2 are similar if their ratio can be written as the product of a rational function and a constant in some extension of K.

Geddes, Keith; Le, Ha; and Li, Ziming. "Differential rational normal forms and a reduction algorithm for hyperexponential functions." Proceedings of ISSAC 2004. ACM Press. (2004): 183-190.