@article{gautschi:1973:aei,
    author = {Gautschi, W.},
     title = {Algorithm 471: {E}xponential integrals},
   journal = {Comm. ACM},
    volume = {16},
      year = {1973},
    number = {12},
     pages = {761–763},
      note = {Includes Algol60 program, maximum accuracy 10S.},
      issn = {0001-0782},
       doi = {10.1145/362552.362557}}