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

Need a real life example that satisfies the property?

  1. May 10, 2013 #1
    I was solving a question which is the following :

    Give examples of 3 sets W,X,Y such that W ε X and X ε Y but W doesn't ε Y . I solved the question by taking the following 3 sets:

    W = {1,2}
    X = { 7 , 8 , W}
    Y = { 3 , 4 , X}

    looking it from the theory point of you I find that W is not a part of Y but the problem is I cannot come up with an example from real life that satisfies this condition. Kindly help me visualize this.

    Thanks in advance.
  2. jcsd
  3. May 10, 2013 #2


    User Avatar
    2017 Award

    Staff: Mentor

    You need some nested set structure.

    A human is an elements of the set of all humans, and the set of all humans is an element of the set of all species. A single human is not a species, therefore it is not in the set of all species.
  4. May 11, 2013 #3
    If human is a set of all humans and the set of all humans belongs to the set of all species is it not the case that the human belongs to the set of all species, representing it via Venn Diagram says that it is but I am not sure what you intend to say is true or not. A good explanation might help
  5. May 11, 2013 #4
    John = {head,body,arms,legs}
    class_01 = {Mary, Lucy, John}

    John is a student, and class_01 is a set of students.
    Is the head of John a student?
    Is the head of John a student of class_01?
    The head of John is not an element of the class_01.
  6. May 11, 2013 #5
    I think this is a wrong example, first of all its not clear whether John is an entity in a bigger set or a set itself, also where are the relationships X ε W and W ε Y in the above example, kindly be clear about the example you mentioned.
  7. May 11, 2013 #6


    User Avatar
    2017 Award

    Staff: Mentor

    It is both, that is the point of Rogerio's and my example, and it is exactly what you are looking for.

    A Venn diagram is logic, not set theory.

    humans={Rogerio, you, me, ...}
    species={humans, cats, dogs, ...} (neglecting that cats and dogs are actually many different species)
    We are not elements of the second set. We are elements of an element of the second set.
  8. May 11, 2013 #7


    User Avatar
    Science Advisor

    In set theory everything is a set. John is a set, which contains head, body, arms, legs.

    W = head. X = John. Y = Class.
    W is an element of X.
    X is an element of Y.
    W is not an element of Y.
  9. May 11, 2013 #8
    Thanks for the replies people I understand the thing exactly now :)
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook