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Newton series, coinductively: a comparative study of composition

Published online by Cambridge University Press:  07 June 2017

HENNING BASOLD
Affiliation:
Radboud University Nijmegen, P.O. Box 9010, 6500GL Nijmegen, The Netherlands, and CWI Amsterdam, P.O. Box 94079, 1090 GB Amsterdam, The Netherlands. Email: h.basold@cs.ru.nl
HELLE HVID HANSEN
Affiliation:
Delft University of Technology, P.O. Box 5015, 2600 GA Delft, The Netherlands. Email: h.h.hansen@tudelft.nl
JEAN-ÉRIC PIN
Affiliation:
Université Paris Denis Diderot and CNRS, 75205 Paris Cedex 13, France. Email: Jean-Eric.Pin@liafa.univ-paris-diderot.fr
JAN RUTTEN
Affiliation:
CWI Amsterdam, P.O. Box 94079, 1090 GB Amsterdam, The Netherlands, and Radboud University Nijmegen, P.O. Box 9010, 6500GL Nijmegen, The Netherlands. Email: jjmmrutten@gmail.com
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Abstract

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We present a comparative study of four product operators on weighted languages: (i) the convolution, (ii) the shuffle, (iii) the infiltration and (iv) the Hadamard product. Exploiting the fact that the set of weighted languages is a final coalgebra, we use coinduction to prove that an operator of the classical difference calculus, the Newton transform, generalises from infinite sequences to weighted languages. We show that the Newton transform is an isomorphism of rings that transforms the Hadamard product of two weighted languages into their infiltration product, and we develop various representations for the Newton transform of a language, together with concrete calculation rules for computing them.