Thanks for the additional responses.

The non-equality of the hash functions is enough to convince me that P(0) 
== 0 is not worth the "convenience" of this type of coercion.

However, just to point out another inconsistency. It seems that coercion is 
currently violating this hash equality in other circumstances.

{{{
sage: CC(3/2) == QQ(3/2)
True
sage: hash(CC(3/2)), hash(QQ(3/2))
(1610645504, 7461864723258187528)
}}}


--

For the other discussion: P(0) = (0:1). I don't have a strong preference 
either way. I have never personally run into any inconsistency issues 
making the assumption of which affine patch is 'default' in dimension 1. I 
find the convenience convenient ;), but do see the potential difficulty in 
tracking down issues this could cause. Actually, I don't find P1(0) = (0:1) 
to be particularly concerning, but P2(0,0) = (0:0:1) (and so one in higher 
dimensions) seems more concerning.

If we were find all the places in Sage where this is used and change them, 
the only place I think a deprecation fits is where this is handled in point 
initialization. My rough feeling of the prevalence of this shorthand seems 
like we would be breaking enough existing code to be concerned about just 
making the behavior change without some kind of user warning through 
deprecation.

Any further thoughts?

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