A nonempty finite set of 
integer matrices for which there exists some product
of the matrices in the set which is equal to the zero
matrix.
Mortal
See also
Integer Matrix, Mortality ProblemExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Mortal." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Mortal.html