a region of space-time, then the probability that the result will be affirmative is the absolute square of a sum of complex contributions, one from each path in the region.* ]{}

This postulate is used to show (among other things) that the most likely paths are those close to the path determined by the least action principle.

No comment is given on the precise mathematical meaning of the terms involved (except for the term “each”); thus we need to see whether we can interpret this in an orthodox way. In the spirit of the standard interpretation of quantum mechanics, we need to assign to each (let us say open and bounded) region $\Omega$ of space-time a projector $\Pi_\Omega$ to the subspace $\Hz_\Omega$ of all wave functions belonging to states where the particle is with certainty in $\Omega$.

Unfortunately, particle positions at different times are represented by operators $x(t)=\exp(iHt)x(0)\exp(-iHt)$ that generally do not commute with each other, with the consequence that it is unlikely that they have common eigenvectors, which would be the elements of $\Hz_\Omega$. Thus, it is very likely that, for most $\Omega$, this subspace consists of zero only; and $\Pi_\Omega$ would vanish. This casts serious doubt on the 