Re: Idempotence and "Replication Insensitivity" are equivalent ?

Jan Hidders wrote:
> You'd split that into computing (minDate, maxDate) and then do some
> post-processing. For (minDate, maxDate) you get:
> - E = (null, null)
> - S(d) = (d,d)
> - A((d1, d2), (d3, d4)) = (MIN(d1, d3), MAX(d2, d4))
> with MIN and MAX defined such that MIN(d, null) = MIN(null, d) = MAX(d,
> null) = MAX(null, d) = d.

This null thingy doesn't make sence:

MIN(MAX(d, null),null) = null (by absorption) MIN(MAX(d, null),null) = d (by applying your rule twice)

It is obvious that you are after neutral elements -oo and +oo such that

MIN(d, -oo) = -oo
MAX(d, -oo) = d
MIN(d, +oo) = d
MAX(d, +oo) = +oo