Ten or forty? : a confusing numerical symbol in the Middle ages / [Charles Burnett].
Note:
Già pubbl. in: Mathematics celestial and terrestrial / Charles Burnett. Halle : Deutsche Akademie der Naturforscher Leopoldina, 2008. Acta historica Leopoldina, p. 81-89
Burnett, Charles. Numerals and arithmetic in the Middle Ages. Aldershot : Ashgate, c2010. [Study IV]