(self)
return self.function.free_symbols.union(set([self.transform_variable])) \
            - set([self.function_variable])
This method returns the symbols that will exist when the transform
        is evaluated.
This method returns the symbols that will exist when the transform
        is evaluated.
This method returns the symbols that will exist when the transform is evaluated .
def free_symbols(self):
        """
        This method returns the symbols that will exist when the transform
        is evaluated.
        """
        return self.function.free_symbols.union(set([self.transform_variable])) \
            - set([self.function_variable])
def free_symbols ( self ) : return self . function . free_symbols . union ( set ( [ self . transform_variable ] ) ) - set ( [ self . function_variable ] )