@misc{indiciae1190b33b354c,
  title = {Lyapunov functionals for a class of wave equations.},
  author = {Buis, G. R. and Vogt, W. G.},
  year = {1968},
  url = {https://ntrs.nasa.gov/citations/19680046530},
  note = {Source identifier: 19680046530}
}