Agreement to agree
The sort of thing a co-calculation agent is expected to do — one that law students learn in lesson one of The Law of Contract one logically cannot be obliged to do — is agree that you will, later, agree on something you cannot be bothered to agree upon just yet. But oh, perfidious syntax of our earthly legal frames! Those who foresee arguments about valuation know there are jagged corals of metaphysical rock not far beneath our footsteps.
This paradox curls back reflexively on itself, for if you agree to it, you must have agreed, but if you have not agreed it, you can’t have.
This sort of thing made Kurt Gödel very famous, but unpopular with Bertrand Russel and David Hilbert. It is an example of the necessary incompleteness of law as a logical system.
An organising principle of the law is that, within identifiable limits prescribed by public law (such as crimes), a citizen is free to agree anything. But the set of things one is free to agree does not include agreement itself. For, if you agree it, you must already be consigned to it, so you are no longer free to agree it. And if you remain free to agree it, then you have not agreed it.