KMain()
  includes ::/StartOS.HC
    includes ~/MakeHome.HC
      includes ~/HomeSys.HC
        calls StartUpTasks()
          includes ~/Once.HC
            calls OnceExe().

AOnce() appends src code to ~/Registry.HC Once/Adam tree, executed at next boot 
by Adam.

Once()  appends src code to ~/Registry.HC Once/User tree, executed at next boot 
by first User term.

At boot, OnceExe(), executes Once/Adam tree, AOnceFlush()s it,
executes Once/User tree and OnceFlush()s.