This is a puzzle from Round 4 of WPF's Puzzle Grand Prix this year.
It's a Slitherlink with the additional rule that "Every Swiss cross-shaped arrangement of five cells must contain at least one cell inside the loop and one cell outside the loop." What I find particularly interesting (i.e. frustrating) about it is how I can't make any progress at all (besides the obvious 2 in the lower left)! I've realized that
the no-Swiss cross rule implies that every cell not on the edge needs at least one of its edges filled in,
but even this has gotten me no further progress. For what it's worth, I solved the previous puzzle (admittedly worth almost a quarter of the points) without using any "special" tactics, i.e. just as a normal Slitherlink with an additional restriction.
I would appreciate some tips on how to get started, as well as some thoughts on how I might have derived them myself.