  The Wheeler-DeWitt equation for the minimally coupled
FRW-massive-scalar-field minisuperspace is written as a two-component
Schr\"odinger equation with an explicitly `time'-dependent Hamiltonian. This
reduces the solution of the Wheeler-DeWitt equation to the eigenvalue problem
for a non-relativistic one-dimensional harmonic oscillator and an infinite
series of trivial algebraic equations whose iterative solution is easily found.
The solution of these equations yields a mode expansion of the solution of the
original Wheeler-DeWitt equation. Further analysis of the mode expansion shows
that in general the solutions of the Wheeler-DeWitt equation for this model are
doubly graded, i.e., every solution is a superposition of two definite-parity
solutions. Moreover, it is shown that the mode expansion of both even and
odd-parity solutions is always infinite. It may be terminated artificially to
construct approximate solutions. This is demonstrated by working out an
explicit example which turns out to satisfy DeWitt's boundary condition at
initial singularity.
