trenchant.org - daily 
Graph Theory
Systems dependent on bidirectional links are usually too complicated to work.
The directed graphs of Ted Nelson hypertext and human relations are too much to understand or implement efficiently.
Unidirectional is simpler but you can't be in love at someone.
Weighted arcs and link types are always cause for complexity. Well intentioned attempts at persistent links give way to the reality of 404s and break-ups.
