Trac #34235: Error in comparing two Symbolic Ring elements

It seems a bug:
{{{
sage: bool(AA(sqrt(2))/pi == sqrt(2)/pi)
TypeError: ECL says: THROW: The catch MACSYMA-QUIT is undefined.
}}}
The following comparison is fine, though.
{{{
sage: bool(AA(sqrt(2)) == sqrt(2))
True
}}}

To fix this, we provide elements of `AA` and `QQbar` with a
`_maxima_init_` method that
- handles the case of elements for which Sage can find a radical
expression and
- raises an error in all other cases.
This is better than sending the unusable print representation of
algebraic numbers (including `?`) to Maxima.

URL: https://trac.sagemath.org/34235
Reported by: yzh
Ticket author(s): Matthias Koeppe
Reviewer(s): Travis Scrimshaw

src/sage/rings/qqbar.py

@@ -4710,6 +4710,34 @@ def radical_expression(self):
             roots = candidates
             interval_field = interval_field.to_prec(interval_field.prec() * 2)
 
+    def _maxima_init_(self, I=None):
+        r"""
+        EXAMPLES::
+
+            sage: maxima(AA(7))
+            7
+            sage: maxima(QQbar(sqrt(5/2)))
+            sqrt(10)/2
+            sage: maxima(AA(-sqrt(5)))
+            -sqrt(5)
+            sage: maxima(QQbar(sqrt(-2)))
+            sqrt(2)*%i
+            sage: maxima(AA(2+sqrt(5)))
+            sqrt(5)+2
+            sage: maxima(QQ[x](x^7 - x - 1).roots(AA, False)[0])
+            Traceback (most recent call last):
+            ...
+            NotImplementedError: cannot find radical expression
+        """
+        try:
+            return self._rational_()._maxima_init_()
+        except ValueError:
+            pass
+        rad = self.radical_expression()
+        if isinstance(rad.parent(), sage.rings.abc.SymbolicRing):
+            return rad._maxima_init_()
+        raise NotImplementedError('cannot find radical expression')
+
 
 class AlgebraicNumber(AlgebraicNumber_base):
     r"""