Where Can I Find the Proof of Asymptotically Helical Trajectory in a Lattice?

[intervoxel]

In the article 'Cellular vacuum' (Int. J. Theor. Phys. 21: 537-551, 1982), Minsky writes: "One can prove that any bounded packet which moves within a regular lattice must have an asymptotically helical trajectory...". But he gives no references whatsoever.
I had no success in a search on the internet, so I ask if someone could help me in this regard.

 

[azntoon]

The reference for this statement is actually provided in the article itself. It can be found on page 548, where Minsky cites the work of P.A.M. Dirac, who first showed that a bounded packet must have an asymptotically helical trajectory in a lattice. The relevant citation is: P. A. M. Dirac, "On the theory of lattices," Proc. R. Soc. London, Ser. A 246 (1958), 326-332.