variables vs arguments

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For symbolic expressions, variables() and arguments() methods return the same result. You can observe this by adding ?? at the end of the function name and taking a look at the code.

sage: var('a,b')
(a, b)
sage: t = a*x^2
sage: t.arguments??
    def arguments(self):
...
        try:
            return self._parent.arguments()
        except AttributeError:
            return self.variables()

For callable expressions, they differ:

sage: t.arguments()
(x,)
sage: t.variables()
(a, x)