Provuso
A proviso with an inbuilt incluso, such that the hand that takes away takes more than the other hand gave in the first place. Ninja stuff.
By this device one states a general principle, then caveats it so comprehensively that the end result bears no correlation at all with one’s original intended. Thus one does not merely weasel out of the original intention, but weasel your counterparty into accepting a 'whole new liability that it cannot possibly have had in mind when discussing your original proposition.
This is not so much weaseling on steroids, but at the hands of a If you were a weasel playing Defender, this would be like hitting the hyperspace button.
See also
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