Two greeter contracts. One referencing a library, the other not.

Greeter.sol

pragma solidity ^0.4.0;

contract GreeterA {
        string greeting;
        uint count;
        address[] greeted;

        function GreeterA(string _greeting) {
                greeting = _greeting;
        }

        function greet() public returns (string) {
                count += 1;
                greeted.push(msg.sender);
                return greeting;
        }
}

library GreeterLib {
        struct Greeting {
                string greeting;
                uint count;
                address[] greeted;
        }

        function greet(Greeting storage self, address who) public returns (string) {
                self.count += 1;
                self.greeted.push(who);
                return self.greeting;
        }
}

contract Greeter {
        GreeterLib.Greeting greeting;

        function Greeter(string _greeting) {
                greeting.greeting = _greeting;
        }

        function greet() public returns (string) {
                return GreeterLib.greet(greeting, msg.sender);
        }
}