Create an E/R diagram which captures the following information, and
then convert it to a relational schema:

* Each Superhero protects one city

* Every supervillain operates out of a secret lair at some location
  (not always a city)

* Some cities host multiple supervillain lairs, some host none.

* Every superhero has a supervillain nemesis.

* A superhero and supervillain always fight in some city.

* Each superhero can team up with other superheroes; supervillains
  form conspiracies.

* Teams of superheroes can battle conspiracies at any location.

* Battles in cities, and nemeses that live in the same city, are
  especially interesting.

Hint: this is pretty straightforward; just take it one step at a time.