  For a graph G, a dominating set D is a subset of vertices in G where each of
the vertices in G is in D or adjacent to some vertex in D. An
open-locating-dominating (OLD) set models a system with sensors to detect an
intruder in a facility or a faulty component in a network of processors. The
goal is to detect and pinpoint an intruder's exact location in a system with a
minimum number of sensors. In this paper, we focus on a variant of an OLD set
called a redundant OLD set and present a proof for the NP-completeness of the
problem of a redundant OLD set.
