4 problems

Let a CSI spacetime be a spacetime all of whose scalar curvature invariants are constant, and let a degenerate Kundt spacetime be a Kundt spacetime whose curvature tensor and all c…

Kundt's conjecture. If all curvature tensors of $(M,g)$ are of aligned type II or more special with respect to some null congruence, then $(M,g)$ is degenerate Kundt: for each poin…

Let a CSI spacetime be a spacetime all of whose scalar curvature invariants are constant, and let a Kundt-CSI spacetime be a degenerate Kundt spacetime whose transverse metric is l…

Let $D$ be the spacetime dimension. A Lorentzian spacetime is $I$-degenerate if it admits a null frame in which all positive boost-weight terms of the curvature tensor and its cova…