- sage: J = random_eja()
- sage: J.zero().operator().inverse()
- Traceback (most recent call last):
- ...
- ZeroDivisionError: input matrix must be nonsingular
+ sage: x = random_eja().random_element()
+ sage: L = x.operator()
+ sage: not L.is_invertible() or (L.inverse().inverse() == L)
+ True