@acer 

Thank you very much for your detailed responses.

They are very helpful, and they solved my problem.

It seems that I did not understand the difference between ifactor() and ifactors() well, which caused the confusion on my side.

Let me appreciate your help again.

@vv 

Very smart!!

Thank you very much for a very quick response, I appreciate it.

@Joe Riel Thank you very much! Now I got a much better understanding of the general difference between substitution and evaluation in Maple. I appreciate your help.

@ecterrab Thank you very much for your very quick response! Your solution worked perfectly, of course.

Thanks again, and now I can move on to the next stage of my calculation.