I have some trouble understanding relatons. Below there is a question that I am working on. I believe that the a) part its correct but I have no idea how to do the b) and c)
As part of a computer security system, you need to control which users have access to which drives. Albert has access to drives X and Z. Belinda has access to drives X, W and Z. Charlotte has access to drives V and W. Eoin has access to drives Z and V. Denoting by U the set of users and D the set of drives,
(a) Give the relation R on U × D which represents this information. (You may use appropriate abbreviations.) MY ANSWER IS BELOW... correct me if I'm wrong
R= {(A,X),(A,Z),(B,X),(B,W),(B,Z),(C,V),(C,W),(E,Z),(E,V)}
(b) Find the combination of projection and inverse projection maps which find those users with access to drive Z.
(c) Find the combination of projection and inverse projection maps which find drives accessible to both Albert and Eoin.
