On 29 Nov., 00:09, John H Palmieri <[email protected]> wrote:
> I think it's this code in sage/rings/polynomial/
> multi_polynomial_ring_generic.pyx:
>
> def __contains__(self, x):
> """
> This definition of containment does not involve a natural
> inclusion from rings with less variables into rings with more.
> """
> try:
> return x.parent() == self
> except AttributeError:
> return False
Is this really what we want? Simply testing equality of the parents? I
don't think that one should drop any coercion!
See Parent.__contains__, which is
def __contains__(self, x):
r"""
True if there is an element of self that is equal to x under
==, or if x is already an element of self. Also, True in
other
cases involving the Symbolic Ring, which is handled specially.
For many structures we test this by using :meth:`__call__` and
then testing equality between x and the result.
The Symbolic Ring is treated differently because it is
ultra-permissive about letting other rings coerce in, but
ultra-strict about doing comparisons.
...
"""
P = parent_c(x)
if P is self or P == self:
return True
try:
x2 = self(x)
EQ = (x2 == x)
if EQ is True:
return True
elif EQ is False:
return False
elif EQ:
return True
else:
from sage.symbolic.expression import is_Expression
if is_Expression(EQ): # if comparing gives an
Expression, then it must be an equation.
# We return *true* here, even though the equation
# EQ must have evaluated to False for us to get to
# this point. The reason is because... in practice
# SR is ultra-permissive about letting other rings
# coerce in, but ultra-strict about doing
# comparisons.
return True
return False
except (TypeError, ValueError):
return False
Cheers,
Simon
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