Method 'one' is supposed to return the identity element of a monoid (or I guess of any magma). String monoids should define it to be the empty string. Not only have they not, the default implementation throws an error:
sage: BinaryStrings().one()
TypeError: Argument x (= 1) is of the wrong type.
Good catch ! Looking at the code, it seems that this class was not touched for a while (created in 2007, last touched in 2009), so i guess nobody took care of it when the one() was created for all monoids (probably through the sategory mechanism). May i encourage you to open a ticket and fix it yourself ?
Actually, it is not correct to say that the monoid is not able to provide an identity element, you can get is as follows:
sage: b('')
sage: b('110') == b('') * b('110')
TrueSince the OP may not have an account, I've taken the liberty of opening http://trac.sagemath.org/ticket/20009 for this.
And indeed there is already a branch on it! Though it needs docstring/tests.
It is now positively reviewed, so the fix should enter the next Sage release.
Asked: 9 years ago
Seen: 351 times
Last updated: Feb 04 '16
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