We show that all domain-wall solutions of gravity coupled to scalar fields
for which the worldvolume geometry is Minkowski or anti-de Sitter admit Killing
spinors, and satisfy corresponding first-order equations involving a
superpotential determined by the solution. By analytic continuation, all flat
or closed FLRW cosmologies are shown to satisfy similar first-order equations
arising from the existence of ``pseudo-Killing'' spinors.Comment: 4 pages, v2:minor improvements, refs added, version to appear in PR