Hi Folks, Here is a recurring problem: Find the difference between what you have versus what you need Here are some examples: 1. Cooking: a recipe calls for this list of ingredients: eggs, flour, milk, chocolate. In my kitchen I have some ingredients. Is there a difference between what the recipe requires versus what I have in my kitchen? 2. Product Inventory: the inventory sheet says one thing. The actual products on the shelf says another. Is there a difference between what the inventory sheet says versus what is actually on the shelves? This recurring problem calls for a nice algorithm to solve it. I am reading a fabulous book, Pearls of Algorithm Design [1]. It describes how to solve the problem. I created Powerpoint slides that expand on the book's description: http://www.xfront.com/Pearls-of-Functional-Algorithm-Design/Chapter1/Find-th... Comments welcome. /Roger [1] http://www.amazon.com/Pearls-Functional-Algorithm-Design-Richard/dp/0521513383/ref=sr_1_1?ie=UTF8&s=books&qid=1305469753&sr=8-1