In this paper, we give a procedure of how to discretize the recursion
operators by considering unified bilinear forms of integrable hierarchies. As
two illustrative examples, the unified bilinear forms of the AKNS hierarchy and
the KdV hierarchy are presented from their recursion operators. Via the
compatibility between soliton equations and their auto-B\"acklund
transformations, the bilinear integrable hierarchies are discretized and the
discrete recursion operators are obtained. The discrete recursion operators
converge to the original continuous forms after a standard limit.Comment: 11Page