[...] the categorial representations will be members of the set defined by the recursive statement: (2) X is a category if: (i) X is a member of the set of primitive categories PC; or (ii) X is of the form V/W, where V and W are categories; or (iii) X is of the form V\W, where V and W are categories.
- Hoeksma (2004), Pag. 194