A Cayley-Hamilton trace identity for 2 x 2 matrices over Lie-solvable   rings
  We exhibit a Cayley-Hamilton trace identity for $2\times2$ matrices with entries in a ring $R$ satisfying $[[x,y],[x,z]]=0$ and 1/2 \in R$. 
Johan Meyer, Jeno Szigeti and Leon van Wyk
math.RA