Note on s-expandable spaces

In [1], the author claimed that “if F = { F j : j ∈ J } is a semi locally finite collection of a topological space, then ⋃ j ∈ J sCl ( F j ) = sCl ( ⋃ j ∈ J F j ) .” We provide an illustrative example to show that this claim is false in general. Then, we investigate the condition under which this equality is true.