Submodular and supermodular games

Can someone please explain to me (with concrete examples) what are submodular and supermodular games, and their related concepts of games of strategic substitutes and strategic complements.

An artificial example using Prisoner's Dilemma would be quite helpful. Thanks in advance.

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The prisoners dilemma is not a very insightful example. The most accessible material I know on these topic are these notes, but it is still not easy. –  Michael Greinecker Jul 17 '12 at 17:27
@MichaelGreinecker, I had a look at similar materials, and struggled to develop an intuitive understanding of the concepts, hence I am asking for a concrete example using a simple game to illustrate the concepts. But thanks for the notes anyway! –  MLister Jul 17 '12 at 17:41
You have two players, Ann and Bob. Both have as their strategy spaces the unit interval $[0,1]$. Also $u_A(x,y)=u_b(x,y)=u(x,y)=xy$, the game is of common interest.
There are two pure-strategy equilibria, $(0,0)$ and $(1,1)$. The game has strategic complements, the payoff functions satisfy increasing differences. If $x>x'$ and $y>y'$, then $$u(x,y)-u(x',y)> u(x,y')-u(x',y)$$ since $(x-x')y> (x-x')y'$ when $(x-x')>0$ and $y>y'$.