Determining if a network of computers is fully connected.

You are given a network of computers and the connections between them.
Your task is to use predicate logic to determine if every computer can directly or indirectly communicate with every other computer in the network.
Given:
1. Computers: A set of computers,{A,B,C,D}.

2. Connections: A set of connections between pairs of computers, {(A,B), (B,C), (C,D)}.

3. Predicates: Computer(x): x is a computer.

4. Connected(x,y): There is a connection between x and y.

5. Reachable(x,y): Computer x can communicate with computer y either directly or indirectly.