@cached_property<EOL><INDENT>def is_conformal(self):<DEDENT>
a, b, c, d, e, f, g, h, i = self<EOL>return abs(a * b + d * e) < EPSILON<EOL>
True if the transform is conformal, i.e., if angles between points
        are preserved after applying the transform, within rounding limits.
        This implies that the transform has no effective shear.