RT Book, Section T1 The Origin of Fuzzy Extensions A1 Bustince, Humberto A1 Barrenechea, Edurne A1 Fernández, Javier A1 Pagola, Miguel A1 Montero De Juan, Francisco Javier A2 Kacprzyk, Janusz A2 Pedrycz, Witold AB Many different kinds of sets have been defined within the framework of fuzzy sets . This paper focusses on those fuzzy set extensions that address the difficulties that experts find in order to build the membership values. In particular, we analyze type-2 fuzzy sets , interval-valued fuzzy sets , Atanassov’s intuitionistic fuzzy sets , or bipolar sets of type-2 and Atanassov’s interval-valued fuzzy sets. After stating a general approach to these extensions, we remark some structural problems in the extension problem and stress some applications for which the results obtained with extens PB Springer SN 978-3-662-43504-5 YR 2015 FD 2015 LK https://hdl.handle.net/20.500.14352/35748 UL https://hdl.handle.net/20.500.14352/35748 LA eng NO Bustince, H., Barrenechea, E., Fernández, J., Pagola, M., Montero, J.: The Origin of Fuzzy Extensions. En: Kacprzyk, J. y Pedrycz, W. (eds.) Springer Handbook of Computational Intelligence. pp. 89-112. Springer Berlin Heidelberg, Berlin, Heidelberg (2015) NO Ministerio de Ciencia, Innovación y Universidades (España) DS Docta Complutense RD 13 jul 2025