Wow! Very interesting indeed! Thank you iikuuk for posting this, and thank you Ajax for the illuminating commentary. I re-created this network just to see if I could get my head around what it is actually doing (alas, my head doesn't seem to stretch that far). That was before Ajax posted the explanation which helps a great deal. There's something truly exciting about feeling way out of one's depth but at the same time hungry to learn. I felt that way about 3D modelling, then about mapping and rendering, then figure creation, and now about this stuff. And the learning is made so much easier by people like you who share your mastery so generously here on the internet - "the university of the third age". Thank you Ob