Problem Set 3 comments are here: [PDF]


Problem Set 3 CommentsProblem Set 3 comments are here: [PDF] 2 comments to Problem Set 3 Comments 

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I am having some trouble with question #5, parts b and c. I was thinking that these two problems could be solved visually with a venn diagram–is this approach valid? If so, how would it be done? I could not seem to make it work, but it seems like it should work, unless intersection here means something different than overlap in a venn diagram.
A Venn diagram might help you visualize what the closure properties mean, but it won’t be very useful in proving them.
Remember that a language is a set of strings, and a language class is a set of languages. The intersection of two languages A and B is the intersection of the two sets, so we could draw this as two intersecting circles in a Venn diagram. The intersection is a new language, which is a point in the setsoflanguages diagram, but it doesn’t tell use where that point is. The questions 5b and 5c illustrate that this point need not be inside the same set as where A and B are.