  We generalize the superposition principle for time-symmetric initial data of
black hole spacetimes to (anti-)de Sitter cosmologies in terms of an eigenvalue
problem $\Delta_g\phi={1/8}(R_g-2\Lambda)\phi$ for a conformal scale $\phi$
applied to a metric $g_{ij}$ with constant three-curvature $R_g$. Here,
$R_g=0,2$ in the Brill-Lindquist and, respectively, Misner construction of
multihole solutions for $\Lambda=0$. For de Sitter and anti-de Sitter
cosmologies, we express the result for $R_g=0$ in incomplete elliptic
functions. The topology of a black hole in de Sitter space can be extended into
an infinite tower of universes, across the turning points at the black hole and
cosmological event horizons. Superposition introduces binary black holes for
small separations and binary universes for separations large relative to the
cosmological event horizon. The evolution of the metric can be described by a
hyperbolic system of equations with curvature-driven lapse function, of
alternating sign at successive cosmologies. The computational problem of
interacting black hole-universes is conceivably of interest to early cosmology
when $\Lambda$ was large and black holes were of mass $<{1/3}\Lambda^{-1/2}$,
here facilitated by a metric which is singularity-free and smooth everywhere on
real coordinate space.
