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I Let A = {1,2,3,4,5,6.} # of many different relations possible

  1. Nov 21, 2016 #1
    How many different relations are possible? Is the question.

    Is the answer the power set of AxA?
    2^36.
     
  2. jcsd
  3. Nov 21, 2016 #2

    fresh_42

    Staff: Mentor

  4. Nov 21, 2016 #3
    HLnt9Fu.png

    I do not understand this too. I am getting an empty set for it.
     
  5. Nov 21, 2016 #4

    fresh_42

    Staff: Mentor

    No, not an empty set, because everything is related to everything without itself. The main diagonal is missing. But I cannot think of a familiar relation.
    Something like: every hand can wash every hand, but not itself. However, what is this mathematically?

    Edit: e.g. the domain of ##(x,y) \longmapsto (x-y)^{-1}##.
     
    Last edited: Nov 21, 2016
  6. Nov 21, 2016 #5

    jbriggs444

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    Science Advisor

    This follow-up question appears to be homework, so I do not want to blurt out what seems to be the expected answer.
     
  7. Nov 21, 2016 #6

    fresh_42

    Staff: Mentor

    Got it.
     
  8. Nov 21, 2016 #7
    no not homework just personal reading. :) I was going over relations once more as I never got it completely the first time. It is a question in this book (and I just noticed that it has solutions there too but they are only for ODD numbered questions
    http://www.people.vcu.edu/~rhammack/BookOfProof/
     
  9. Nov 21, 2016 #8

    jbriggs444

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    The difficulty is that the the "homework" umbrella on these forums encompasses both material that is actual homework and material that is homework-like, even though it may not be an assigned homework problem in a course that is currently being taken.

    See the sticky posting at the top of this forum: https://www.physicsforums.com/threa...mework-or-any-textbook-style-questions.42532/
     
  10. Nov 21, 2016 #9

    Mark44

    Staff: Mentor

    As jbriggs444 said, your post falls under the heading of "homework," which includes problems from books even if you are not in a course that uses that textbook.
     
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