パーセント記号
Smith, D.E. (1898), Rara Arithmetica: a catalogue of the arithmetics written before MDCI, with description of those in the library of George Arthur Plimpton of New York, Boston: Ginn, https://archive.org/details/raraarithmeticac00smituoft
Smith, D.E. (1925), History of Mathematics, Boston: Ginn