  Let us denote p(x|K) the space density of the points where identical
particles of some kind, e.g. pi+ mesons, with momentum K are produced. When
using the HBT method to determine p(x|K) one encounters ambiguities. We show
that these ambiguities do not affect the even cumulants of the distribution
p(x|K). In particular, the HBT radii of the homogeneity regions, which are
given by the second order cumulants, and the distribution of distances between
the pairs of production points for particles with momentum K can be reliably
measured. The odd cumulants are ambiguous. The are, however, correlated. In
particular, when the average position <x>(K) is known as a function of K there
is no further ambiguity.
