svoid test_FactStore() {
  PhilosophyBot1 bot = new([[
    $x weighs $y
      => delete all (last time $x weighed $z)
       & store      (last time $x weighed $y)
  ]]);
  bot.parseProgram();
  new SimpleFactStore fs;
  philosophyBot1_factStore(bot, fs);
  bot.addFact("x weighs (50 pounds)");
  bot.think();
  print(fs.facts);
}