What does this symbol mean?

[SamanthaMFR]

I was wondering what that symbol on top of the B means (I am studying set theory)

 

[Ishuda]

View attachment 5093 I was wondering what that symbol on top of the B means (I am studying set theory)

In set theory, I have seen the overbar used quite often as 'the complement of' so this would be the complement of the complement of B which is just B. Some use the superscript c as complement and thus the B with the double overbar would be the same as (B^c)^c