@article{whitehead:1911:gfb,
    author = {Whitehead, C. S.},
     title = {On a generalization of the functions $\mathrm{ber}$ x, $\mathrm{bei}$ x,
               $\mathrm{ker}$ x, $\mathrm{kei}$ x},
   journal = {Quart. J. Pure Appl. Math.},
    volume = {42},
      year = {1911},
     pages = {316–342},
     zblno = {42.0490.01}}