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Tzwyvel Arithmeticae opuscula duo . Book Tzwyvel Theodoricus Arithmeticae opuscula duo Kln lat it Arithmetice opuscula duo Theodorici Tzwiuel de numerorum praxi que algorithmi dicuntur vnum de integris per figurarum more alemanorum deletionem Alterum de proportionibus cuius vsus frequens in musicam harmonicam Seuerini Boetij Kln