The Voynich Ninja

I think a rough check of whether characters are interchangeable or not may be done by calculating digram frequency matrices and see if they are in concordance or not. Like, for characters X and Y and any Z, look if XZ is as frequent as YZ (provided, of course, that frequency of Y is normalized to that of X).

voynich.nu is currently down for me, so I'm not able to have a check if this was ever done.