What's right topology for a concave polygon? I have a problem with the topology of a concave corner in a text I have traced. The corner must be sharp so I placed some proximity edges to avoid the subsurf modifier smoothing.

This is how I managed a convex area. I don't know if the topology is correct, but I don't have any problem:




I tryed something similar in a concave area, cutting through one more loop:




When the subsurf is applied, the result is really bad. It seems like there is a hole somewhere, or some rogue faces, but it's not. Everything is "ok".




I can't understand why this happens. It's even all quads.
There is clearly something I don't understand, so I hope to receive some help.

Thank you in advance :)
If I understand you correctly you want to get rid of the soft edges that are produced by the subsurf/multires modifier? You may want to look if you can fix that by setting the mean crease in the object's option bar to 1. 

You possibly need to play around with the value for different edges but usually it gets the job done.