  We propose a definition of diversification as a binary relationship between
financial portfolios. According to it, a convex linear combination of several
risk positions with some weights is considered to be less risky than the
probabilistic mixture of the same risk positions with the same weights. It
turns out to be that the proposed partial ordering coincides with the
well-known second order stochastic dominance, but allows to take a look at it
from another perspective.
