[3. Schrödinger equations.]
A brief recapitulation.
A quantum state is described by a complex function Ψ. Every physical quantity is defined
by a quantum operator which satisfies the first Schrödinger equation. The eigenvalues
determine the possible value of the quantity. The function Ψ is represented as a sum of
the eigenfunctions; the expansion coefficients give the probability of every possible value
of the quantity. The time dependence of Ψ is described by the second Schrödinger equation,
which determines Ψ at every time. Thus the probability of every admissible value of every
physical quantity is determined.
