implement product of posets

[fchapoton]

There currently lacks an implementation of the (cartesian) product of posets.

sage: P2=Posets.ChainPoset(2)

sage: P4=Posets.ChainPoset(4)

sage: Q=P2.product(P4)

This should return a poset with 8 elements, with Hasse diagram a 2 x 4 grid.

It would be nice to have a fast enough procedure for this.

Depends on #12770

CC: @fchapoton @sagetrac-sage-combinat

Component: combinatorics

Keywords: poset, product

Author: Frédéric Chapoton

Reviewer: Itai Bar-Natan

Merged: sage-5.1.beta1

Issue created by migration from https://trac.sagemath.org/ticket/12831

[fchapoton]

Dependencies: #12770

[fchapoton]

comment:3

Some typos need to be corrected..

[fchapoton]

Attachment: trac_12831-product_of_posets-fc.patch.gz