Toggles of Openings, and a New Family of Idempotent Operators on Partially Ordered Sets.

Christian Ronse Toggles of Openings, and a New Family of Idempotent Operators on Partially Ordered Sets. 99-128 1992 3 Appl. Algebra Eng. Commun. Comput. db/journals/aaecc/aaecc3.html#Ronse92