Vol. 39 Num. 3 (2019) - front cover0 Einat Heyd-Metzuyanim Dialogue between discourses: beliefs and identity in mathematics education ABSTRACT 2 Kyriakos Petakos Communication: Is mathematical productivity a quasi-OCD?9 Lluis Albarracin , Jonas B. Ärlebäck Communication: Characterising mathematical activities promoted by Fermi problems10 Amir Asghari Communication: Signed numbers and signed letters in algebra13 Nicholas Wasserman Duality in combinatorial notation ABSTRACT 16 Anderson Norton An Erlangen program that empowers students' mathematics ABSTRACT 22 Asmund Lillevik Gjære , Natalia Blank Teaching mathematics developmentally: experiences from Norway ABSTRACT 28 Justin Dimmel , Amanda Milewski Scale, perspective and natural mathematical questions ABSTRACT 34 Rob Wieman Communication: But that's obvious: launching and persistent pitfalls41 Arthur Bakker Communication: What is worth publishing? A response to Niss43 Jinfa Cai , Stephen Hwang Communication: Constructing and employing theoretical frameworks in (mathematics) education research45 David A. Reid Editorial48 - Volume index50 - Contributor affiliations and contact information52