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It is shown that nonlocality gives rise to an undecidable proposition, meaning it cannot be proved true nor proved false from the usual assumptions, but is independent of them. A variation on the usual thought experiment is considered in which the observers are timelike separated, but the nonlocality fails to become a “precognition” effect because of this independence result.

An allegation of a flaw in the theory developed by Dirac for the Hamiltonian formation of singular dynamical systems is denied. It is shown that the Dirac theory is perfectly correct, and adequate as a Hamiltonian theory-but also there is a gain to be had by looking at the structural features involved in the original Lagrangian picture, including those 'canonical' features necessary for the purpose of quantisation; it is indicated how the controversy about first-class secondary constraints may be examined in this way.

A new approach is suggested to the teaching of analytical dynamics, in which the Lagrangian and Hamiltonian pictures are presented simultaneously. It is used to explain the connection between symmetries and conservation laws, and the passage to quantisation.

Bondi’s Newtonian Poynting Vector is extended to other ‘Bondi-type’ conserved quantities, which are also derived by variational methods. By means of the technique of Seliger & Whitham it is shown that they are the expressions which arise most naturally in contexts concerned with the equations of motion. The pseudo-tensor derived from the Lagrangian R √(— g) is the corresponding expression in General Relativity; direct calculation verifies that it tends to Bondi’s vector in the Newtonian limit.