  We show that any unitary transformation performed on the quantum state of a
closed quantum system, describes an inner, reversible, generalized quantum
measurement. We also show that under some specific conditions it is possible to
perform a unitary transformation on the state of the closed quantum system by
means of a collection of generalized measurement operators. In particular,
given a complete set of orthogonal projectors, it is possible to implement a
reversible quantum measurement that preserves the probabilities. In this
context, we introduce the concept of "Truth-Observable", which is the physical
counterpart of an inner logical truth.
