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Hello all. I'm working with variational calculus in sage and working with complicate expression F of a lot of variables declared with var. I used var to declare both variables and constants. My problem is that I have to know the exact number of variables which some generic expression depends. By this reason the member function variables of an expression does not work, i.e., it returs both variables and constants because them was declared with var function. I'm wondering if there is some type of variable in sage that can act as a variable to construct an expression and don't be returned by the variables member function.