Hesitant fuzzy sets applied to BCK/BCI-algebras

We define a hesitant fuzzy BCK/BCI-algebra and obtain some of its properties. Next, we introduce the concept of hesitant fuzzy ideal and obtain some of its properties and give some examples. Finally, we define a hesitant fuzzy positive implicative ideal, a hesitant fuzzy implicative ideal, a hesitant fuzzy commutative ideal and investigate some of its properties, respectively and their relations. In particular, we give characterizations of hesitant fuzzy positive implicative ideal, a hesitant fuzzy implicative ideal and a hesitant fuzzy commutative ideal, respectively. 2010 AMS Classification: 06F35, 03G25, 03E72