Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Question about Properties of Relations

  1. Dec 9, 2009 #1
    1. The question is: P on the set, A, of all people, where xPy means x is a parent of y.



    2. Relevant equations - None



    3. Attempts at a Solution Here is where I am confused. Reflexivity is defined by aRa. So I am unclear what to do with more than one variable. So in this question, do I examine if xRx? That is to say is x a parent of x? If that is the case, then the answer is clearly no. I am just unsure of how to deal with reflexivity.

    I am ok with symmetry and transitivity.
     
  2. jcsd
  3. Dec 9, 2009 #2

    Mark44

    Staff: Mentor

    Can x be the parent of x? IOW, can someone be his or her own parent?
     
  4. Dec 9, 2009 #3
    Okay, so am I correct in what to do with reflexivity in this question? It is obviously absurd that x can be the parent of x. Where I am unclear is if that is the question I need to be asking vis-a-vis reflexivity.
     
  5. Dec 9, 2009 #4

    Mark44

    Staff: Mentor

    I thought I was pretty clear - the relation P is not reflexive.
     
  6. Dec 9, 2009 #5
    You were pretty clear. I am just at the very end of my proof writing class, and it has me pretty jumpy. Thanks for your help.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook