@article{10_4064_ap_19_2_123_135,
     author = {James C. Lillo},
     title = {The functional equation $f^2(x) = g(x)$},
     journal = {Annales Polonici Mathematici},
     pages = {123--135},
     publisher = {mathdoc},
     volume = {19},
     number = {2},
     year = {1967},
     doi = {10.4064/ap-19-2-123-135},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap-19-2-123-135/}
}