@article{stefanik2013double,
  author = {Stefanik, D. and {\v{S}}imkovic, F.},
  title = {{DOUBLE} {FERMI} {MATRIX} {ELEMENT} {WITHIN} {PERTURBATION} {THEORY}},
  journal = {ROMANIAN JOURNAL OF PHYSICS},
  volume = {58},
  number = {9-10},
  pages = {1251--1257},
  year = {2013},
  issn = {1221-146X}
}