@article{najfeld_lakin_2003, 
  title={$L$-derivative of an approximate solution to $\Phi '=\bold A(t)\Phi $: series and product formulae for left corrections}, 
  volume={61}, 
  DOI={10.1090/qam/1999836}, 
  publisher={American Mathematical Society (AMS)}, 
  author={Najfeld and Lakin}, 
  year={2003}, 
  month={Sep}
  }