For each of the following languages, what is the $\backslash$emph$\{$smallest$\}$ set of languages that it

belongs to$?$ For each language just choose one from: $$\backslash \{$$$``$regular$\text{'}\text{'},``$context$-$free'$\text{'},``$decidable$\text{'}\text{'},``$recognizable$\text{'}\text{'}$$$\backslash \}$$$.$

$$\backslash \{$w$\backslash$$z ~$|$~ w$,$z$\backslash$in$\backslash \{$a$,$b$\backslash \}^*\backslash$text$\{$ and $\}$ w eq z $\backslash \}$$