How about primitive composition? For example we could implement set subtraction using union and intersect. But from the slide, it seems like we should avoid implementing set subtraction if set union and set intersect were already primitives...
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The next slide explains that we want the primitives to compose well. In this case, having set union and intersect makes it easy to compose the 2, and not having set difference makes the system simpler.
How about primitive composition? For example we could implement set subtraction using union and intersect. But from the slide, it seems like we should avoid implementing set subtraction if set union and set intersect were already primitives...
The next slide explains that we want the primitives to compose well. In this case, having set union and intersect makes it easy to compose the 2, and not having set difference makes the system simpler.