This is a preface
Bibliographical noteThis article is in press. Full citation details of the article will be added when it has been published in print.
NOTICE: this is the author’s version of a work that was accepted for publication in Science of
Computer Programming. Changes resulting from the publishing process, such as peer
review, editing, corrections, structural formatting, and other quality control mechanisms
may not be reflected in this document. Changes may have been made to this work since it
was submitted for publication. A definitive version was subsequently published in Science of
Computer Programming (2014) In Press. DOI 10.1016/j.scico.2014.04.007