)clear all

   All user variables and function definitions have been cleared.
variables (2*x+1/x)$DMP([x], EXPR INT)

(1)

variables (2*y+1/y)$DMP([y], INT)

   There are 4 exposed and 7 unexposed library operations named 
      variables having 1 argument(s) but none was determined to be 
      applicable. Use HyperDoc Browse, or issue
                            )display op variables
      to learn more about the available operations. Perhaps 
      package-calling the operation or using coercions on the arguments
      will allow you to apply the operation.

   Cannot find a definition or applicable library operation named 
      variables with argument type(s) 
                        Fraction(Polynomial(Integer))

      Perhaps you should use "@" to indicate the required return type, 
      or "$" to specify which version of the function you need.

Possible Explanations: see SandBoxPolynomialQuizExplained