@article{RSMUP_1969__42__201_0,
     author = {Schaefer, D. J.},
     title = {On multiplicity functions and {Lebesgue} area},
     journal = {Rendiconti del Seminario Matematico della Universit\`a di Padova},
     pages = {201--207},
     publisher = {Seminario Matematico of the University of Padua},
     volume = {42},
     year = {1969},
     mrnumber = {276444},
     zbl = {0234.28011},
     language = {en},
     url = {http://archive.numdam.org/item/RSMUP_1969__42__201_0/}
}