tricky with Permaculture and specialization. I'd almost have to say Bill and David's two books are the only generalized Manuals... after that it get pretty focused. Alternative Economics could be considered just as central as say, food forests... but if you live in Hong Kong, Permaculture is not inaccessible, just different... Window gardens and Patio Permaculture could be the main thing. Was wondering about underground permaculture.... like literally. What if you had to be sustainable in a bunker for a year/indefinately? Just a thought exercise... I really dunno where to draw the line so I tend to branch out with vigor and reckless enthusiasm. But the 'philosophy' is important. One way I heard it... "if it doesn't care for people, the Earth or return the surpluses back into the system... it's not Permaculture' an easy starting point I spose.