It seems that you can select pretty much any set of wall segments and say “You have to pass through one of the gaps between the edges of the map, these wall segments, and the gaps between them”.
Yes, that’s exactly correct. Of course, not all sets of wall segments are equally useful—you want a set with relatively few/narrow gaps. When searching for a barrier, that means searching for a wall-path which jumps relatively few gaps—i.e. a dual-space-path which violates relatively few dual-space-constraints.
Yes, that’s exactly correct. Of course, not all sets of wall segments are equally useful—you want a set with relatively few/narrow gaps. When searching for a barrier, that means searching for a wall-path which jumps relatively few gaps—i.e. a dual-space-path which violates relatively few dual-space-constraints.