@article{CanforaSchmidt2003,
  author    = {Canfora, Fabrizio and Schmidt, Hans-J{\"u}rgen},
  title     = {Vacuum solutions which cannot be written in diagonal form},
  year      = {2003},
  abstract  = {A vacuum solution of the Einstein gravitational field equation is shown to follow from a general ansatz but fails to follow from it if the symmetric matrix in it is assumed to be in diagonal form.},
  language  = {en}
}
@article{Schmidt2003,
  author    = {Schmidt, Hans-J{\"u}rgen},
  title     = {The square of the Weyl tensor can be negative},
  year      = {2003},
  abstract  = {We show that the square of the Weyl tensor can be negative by giving an example},
  language  = {en}
}