beta-normalization may loop infinitely after a stripmine transformation

[ftynse]

For the beta structure [0,0,0], [0,0,1], [0,0,2], [0,1,0] performing stripmine([0,1],1,1) makes the beta-normalization loop indefinitely.

Supposedly, it transforms [0,1,0] into [0,0,1,0] resulting in the loss of prefix-free property of the beta-tree. The correct new beta vector should look like [0,1,0,0], but the general case has to be clarified.