  Zurek's derivation of Born's rule using envariance (invariance due to
entanglement) is considered to capture the probability in full generality, but
only as applied to measurement of a quantum observable. Contrariwise, textbook
formulations of Born's rule begin with a pure state of a closed, undivided
system. The task of this study is to show that a rearrangement of the Zurek
approach is possible in which the latter is viewed as giving the probabilities
for Schmidt states of an arbitrary composite state vector, and afterwards it is
extended to probabilities in a closed, undivided system. This is achieved by
determining simultaneously probability and measurement based on the fact that
the physical meaning of probability and that of measurement are inextricably
dependent on each other.
