Unbounded half-space region consumed by RegionMember/RegionDistance/RegionDimension
HalfSpace[n, p]
HalfSpace[n, c]
Graphics[HalfSpace[{2, 1}, {0, 0}]]
→ -Graphics-Graphics3D[HalfSpace[{-1, -1, 1}, {0, 0, 0}]]
→ -Graphics3D-Show[ill, Graphics3D[HalfSpace[{-1, 0, 0}, -1]]]
→ -Graphics3D-