Re: header part of the value?

On 28 feb, 17:27, Tegiri Nenashi <TegiriNena..._at_gmail.com> wrote:
> On Feb 28, 12:03 am, Jan Hidders <hidd..._at_gmail.com> wrote:
>
>
>
> > On 28 feb, 04:32, Tegiri Nenashi <TegiriNena..._at_gmail.com> wrote:
>
> > > On Feb 27, 7:08 pm, Marshall <marshall.spi..._at_gmail.com> wrote:
>
> > > > It appears to me as if you are viewing the
> > > > equation "x + 3 = y" as having 3 as the free variable, and
> > > > x and y as constants! Whereas I would consider it much
> > > > more natural to consider x and y as free variables, or
> > > > parameters, or attribute names (they are all the same)
> > > > and 3 and 5 as constants.
>
> > > Well, the case with two variables in the header is tricky. First,
> > > define union and join then we can talk about it:-)
>
> > How about: the union is the logical disjunction of the equations and
> > the join is the logical conjunction of the equations?
>
> Can you please apply your definition on the example:
>
> Q:
> x + 3 = y \/
> x + 5 = y
> R:
> x + y = 7
>
> What is the header of the join, is it {"x+...=y", "x+y=7"}, or is it
> {"x=...", "y=..."}. What is the header of the union?

In both cases {x,y}.

• Jan Hidders