The concept of hesitant union (⋓) is introduced. Using this, the notions of ⋓-hesitant fuzzy subalgebras and ⋓-hesitant fuzzy ideals are introduced and several properties are investigated. Relations between ∪-hesitant fuzzy subalgebras (resp. ideals) and ⋓-hesitant fuzzy subalgebras (resp. ideals) are considered. Relations between a ⋓-hesitant fuzzy subalgebra/ideal and its lower level set are investigated. Characterizations of ∪-hesitant fuzzy subalgebras/ideals are discussed. Given a subalgebra (resp., ideal) A of a BCK/BCI-algebra X, a ⋓-hesitant fuzzy subalgebra (resp., ideal) is established.
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