@Mahkitah : Interessant, thanks for the expression "edge logic", I didn't know how it's named in english (in french, "méthode des coins")

Thanks everybody.
@Jmestradaabud : Does "2D logic" only refer to "edge logic" ? I thought "2D logic" encompassed other methods like "smile logic" (?)

@Jmestradaabud : No need to apologize :) Questions of logic are interessant questions. In the english site, I only saw the dichotomy single-line logic/2D-logic ; now I know edge logic. But in the french site, we developped "principe d'alternance" ("smile logic" which is a generalization of the "smile pattern"), "wave logic", and "bound logic". For the moment, I didn't post hanjie which needs these methods cause I don't know exactly how it's considered in this site. So, each discussion about logic helps me to progress ;)
By the way, I found this link after reading Mahkitah's comment : http://webpbn.com/index.cgi?page=solving.html .