moving "is_integrally_closed" to the category setup.

[fchapoton]

This is moving a method from the auld Ring class to the category setup.

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[vincentmacri]

I'm not too familiar with the Sage category setup, but why isn't the default implementation to raise a NotImplementedError? It looks like that was the previous behaviour.

[fchapoton]

yes, indeed, that's another possibility and that was the previous behaviour. We can also decide to say "False" if there is no specific reason known for the property in question to hold. I have no strong opinion.

[vincentmacri]

yes, indeed, that's another possibility and that was the previous behaviour. We can also decide to say "False" if there is no specific reason known for the property in question to hold. I have no strong opinion.

I feel that it's better to raise an error than report a potentially incorrect result.

[vincentmacri]

LGTM

[mantepse]

I'm overriding the needs-review bot.