Re: sets of t_POLMOD

[Karim Belabas <Karim.Belabas@math.u-bordeaux.fr>]

* Max Alekseyev [2018-02-22 16:12]:
> Hello!
> 
> I observe the following behavior in Version 2.10.0 (development 21603-bef585b)
> 
> ? S = Set( [Mod(0,x^2+1)] )
> %1 = [Mod(0, x^2 + 1)]
> ? S*x
> %2 = [Mod(0, x^2 + 1)]
> ? setintersect(S,Set(S*x))
> %3 = []
> 
> Isn't this a bug?

Not really: S and S*x *are* different [ inspect with dbg_x() or \x ].

They are printed the same way and will test equal (==, mathematical
equality allowing coercion), but not identical (===, typed equality) :

(16:16) gp > S = Set( [Mod(0,x^2+1)] )
%1 = [Mod(0, x^2 + 1)]
(16:16) gp > S==S*x
%2 = 1
(16:16) gp > S===S*x \\ the reason is that lift S*x is Pol(0), not 0
%3 = 0
(16:16) gp > setintersect(S, simplify(S*x))
%4 = [Mod(0, x^2 + 1)]

Cheers,

    K.B.
--
Karim Belabas, IMB (UMR 5251)  Tel: (+33) (0)5 40 00 26 17
Universite de Bordeaux         Fax: (+33) (0)5 40 00 21 23
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