So what does Lite mode mean? I finally decided (on the grounds that it was too difficult to do anything more sophisticated) that you can define and save a game, but only one, and then try to solve it until it's solved, either by you or by the app. It's then deleted, and you can either re-enter the game or define a new one.
In addition, the Lite version doesn't give you access to the range of solving tools included, for Killer SuDoku games, in the full version. It doesn't mean you can't solve these games, only that you have to try harder and expend more brain power on it.
The differences between the two versions are now fairly substantial, and there is a need for a separate Help file and set of screen shots to accompany the Lite version.
We've had two of the grandchildren staying here over the last few days, and it turns out that they're extremely competitive about who can solve a Fiendish or Difficult one the fastest. (SuDoku games, not Killer ones, but the same concept will apply to Killer when they're older.) Now that's something you need the Full version for, as you can save a game and everyone can have a go at solving it so see who's the fastest. It must be the same game, as there's little to be gained by comparing the time taken to solve two distinct Fiendish games.
I'm also taking the opportunity to tidy up the Windows VB version, in particular the way it uses the registry to store user-related data such as the list of sources or difficulty levels. It's now much more in line with the approach taken on Android.