When you are faced with an apparently impossible situation, an in-built self-contradiction, I suggest that you try four different methods of resolving the problem, and you may well be able to think of others for yourself.

Now there is one strategy that you should firmly avoid, and unfortunately it looks superficially a highly attractive one. It is the first thing that would normally occur to you. You try to think out a compromise. Well, don't. Later on, when you have found the real solution, a certain element of compromise may be necessary over details. That is in order; but compromise over fundamental requirements is the escape of the faint-hearted, and you don't escape in the long run.

My first suggestion is that, instead, you should try to make one of the conflicting parties change sides. You are faced with conditions that can be divided into rival groups, like two armies facing each other, and you must stop the war by finding enough deserters who will cross over.

You will remember that we used earlier the illustration of the evolving complexity and efficiency of cylinder head design. One of the most famous designs of the post-war years was that of the 4.2-litre Jaguar engine, shown in Fig. 20. Its efficiency sprang from the use of a spherical cylinder head, with inclined valves and two overhead camshafts.