Some of this looks good but take another look. For example, if y is lubA and y lt; c then this does not necessarily imply y is an element of A. Try...

I need help on the following problem: I completed the problem in the first picture and i have to fix it based on the second picture.

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2.6.2(20: Some of this looks good but take another look. For example, if y is lubAand y < c then this does not necessarily imply y is an element of A. Try this: clearlyA is bounded above by c and thus lubA must exist. By definition of lub we knowthen that lubA <= c. Show why lubA < c yields a contradiction.