@Carl Love Yes, it works. Thank you very much!

@Carl Love Thank you very much!

@Carl Love Thank you very much. I copied your codes and try to run it on Maple2019. But it has some error information: Error, invalid arrow procedure.

I attached a picture. Do you know how to solve this problem?

@Carl Love This one I also consider it as a monomial. The expressions I considered are polynomials in Y_{i,s}, i, s are some integers, Y[i,s] can have rational exponents. All other variables are considered as variables in the coefficients. For example, sin(t+x)*x*Y[1,3]^(1/3) is a monomial. sin(t+x)*x*Y[1,3] + 1 is a polynomial (not a monomial), sin(t+x)*x*Y[1,3]^(-1) + Y[2,3] is a polynomial (not a monomial). (3+x)*Y[1,3]^(1/2) is a monomial. I am sorry that I didn't descibe the problem correctly in the beginning. Thank you very much.

@Carl Love Thank you very much! Your definition of the function Exponent is perfect!

@Carl Love Yes, I consider them as monomials. Thank you very much!

@vv Thank you very much!

@tomleslie Thank you very much! But this does not work for Y[1,3]. op(2, Y[1,3]) is not 1.

@tomleslie Thank you very much! Is there a way to let it return ture for expressions of the form sqrt(t)*Y[1, -3]*Y[2, -6]? Also return false for a term of the form Y[1,3]+Y[2,3]^{2}. I would like to return true for a term without plus, minus and return false otherwise. 

@vv thank you very much for your help.