Re: subst() broken

[Bill Allombert <allomber@math.u-bordeaux.fr>]

> I cannot "remember" it because priorities are not documented.  I find
> some unintelligible hints (in the section "Polmods"); some other
> *hints* in "Type t_POLMOD (polmod)' (without definition of what is a
> priority); and a kinda-definition in "PARI variables" (without
> mentioning the relation to the time flow).

Yes you can, since we already discuss it in this mailing list :-)

> > Probably you mean (1+y)*Mod(1,z), but it is not the same thing:
> > it is a polynomial not a POLMOD.
> 
> I have no slightest idea what you mean by this sentence.  Can it be
> expressed algebraically, or it is just some "implementation detail"?
Both.

(1+y)*Mod(1,z) is an object living in the ring (Q[Z]/(Z))[Y],
so it is a polynomial in Y whose coeffcients are cosets in Z.

Mod(1+y,z) is an object living in Q(Z)[Y]/(Z) so it is a coset,
but the ideal (Z) being trivial because Z is invertible, this quotient
is the null ring.

Hopes I have answered your question.

Bill.