Long ago, when the world was young, I passed an O-level in which this subject cropped up, but Time has erased much of what I once knew. I have a complete initial grid fill and can see the three initial entities and I know what I must draw ... but the 14 extra words mean nothing to me, and thus I can't see what must be changed (although I know where). A gentle guide to rolling back the clouds of age would be welcome.