Write datalog queries for all of the following

Consider a database with the following schema.

LIKES(drinker,beer); /* key: all columns */

FREQUENTS(drinker,pub); /* key: all columns */

SERVES(_pub,beer_,cost); /* key: (pub,beer) */

1. Find pubs that serve some beer that Joe likes.

2. Find drinkers who frequent pubs where they can get a drink for less

than $3

3. Find drinkers who like some beers but do not frequent any pubs.

4. Find pubs that serve every beer that Joe likes.