  This paper is a sequel of the series of papers [gr-qc/9409010, gr-qc/9505034,
gr-qc/9603022], being an immediate continuation and development of the latter
of them. In the Friedmann universe, the equation $\Omega_0=2q_0$ holds
($\Omega$ is density parameter, $q$ is deceleration parameter, and subscript 0
indicates present-day values), which gives rise to the problem of the missing
matter as observational data give $\Omega_0<2q_0$. In the cosmic-length
universe, $\Omega_0=2q_0- L/R_0^3H_0^2$ ($R_0$ is the radius of the universe,
$H_0$ is Hubble constant), which lifts the problem. The cosmic length, $L=const
\approx 1/H_0$, is the infimum of the set of maximal radii of a closed
universe.
