  The theory of pictures between posets is known to encode much of the
combinatorics of symmetric group representations and related topics such as
Young diagrams and tableaux. Many reasons, com-binatorial (e.g. since
semi-standard tableaux can be viewed as double quasi-posets) and topological
(quasi-posets identify with finite topolo-gies) lead to extend the theory to
quasi-posets. This is the object of the present article.
