ELA, Volume 13, pp. 56-71, February 2005, abstract.

Focal Power

Robert E. Hartwig and John Maroulas

The properties of a 2x2 block matrix M over a field
for which (M^k)_{11} = (M)_{11}^k are examined. 
This "fire-wall" property will be characterized by the 
vanishing of the sequence of moments F_i = C D^i B.