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Unformatted text preview: (b) Is there a least element? A greatest element? (c) Find a lower bound for 60 , 72. (d) Find all upper bounds for 2 , 9 (e) Is this a lattice? 5. A poset is called wellfounded if there is no inﬁnite descending chain of elements. A poset is called wellordered if every nonempty subset has a least element. Consider the poset Z , ± given by x ≺ y iﬀ  x  <  y  (a) Show that this is a poset (b) Show that it is wellfounded, but not wellordered. 6. Show that the lexicographic order on the product of two wellfounded posets is wellfounded. 7. Show that the lexicographic order on the product of two wellordered posets is a wellordering....
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This note was uploaded on 09/10/2009 for the course MATH 55 taught by Professor Strain during the Summer '08 term at Berkeley.
 Summer '08
 STRAIN
 Math

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