# Antisymmetric Relations

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• Feb 28th 2010, 10:14 PM
JazzGuitarist01
Antisymmetric Relations
I am having a little trouble wrapping my head around this. I understand
the Reflexive, Symmetric, and Transitive properties just fine but do not understand the Antisymmetric examples my textbook gives.

Consider the following relations on {1,2,3,4}

R5={(1,1),(1,2),(1,3),(1,4),(2,2),(2,3),(2,4),(3,3 ),(3,4),(4,4)}
R6={(3,4)}

If anybody could help explain why the above satisfy the Antisymmetric property I would really appreciate it.
• Feb 28th 2010, 10:19 PM
Drexel28
Quote:

Originally Posted by JazzGuitarist01
I am having a little trouble wrapping my head around this. I understand
the Reflexive, Symmetric, and Transitive properties just fine but do not understand the Antisymmetric examples my textbook gives.

Consider the following relations on {1,2,3,4}

R5={(1,1),(1,2),(1,3),(1,4),(2,2),(2,3),(2,4),(3,3 ),(3,4),(4,4)}
R6={(3,4)}

If anybody could help explain why the above satisfy the Antisymmetric property I would really appreciate it.

If it's anti-symmetric then if $x\leqslant y$ and $y\leqslant x$ then $x=y$.

So, does that happen here?
• Feb 28th 2010, 10:43 PM
JazzGuitarist01
I'm not sure I follow you correctly.

So example R6 is Antisymmetric because it follows
if http://www.mathhelpforum.com/math-he...3789366b-1.gif and http://www.mathhelpforum.com/math-he...d589218b-1.gif then http://www.mathhelpforum.com/math-he...57631d16-1.gif

But how does R6 satisfy that? In that example isn't x not equal to y?
• Feb 28th 2010, 10:48 PM
Drexel28
Quote:

Originally Posted by JazzGuitarist01
I'm not sure I follow you correctly.

So example R6 is Antisymmetric because it follows
if http://www.mathhelpforum.com/math-he...3789366b-1.gif and http://www.mathhelpforum.com/math-he...d589218b-1.gif then http://www.mathhelpforum.com/math-he...57631d16-1.gif

But how does R6 satisfy that? In that example isn't x not equal to y?

R6 satisfies this vacuously. We only have that $3\leqslant 4$. There is no other info to check.
• Feb 28th 2010, 11:12 PM
JazzGuitarist01
Oh ok.

I still feel a little unsure, so I am gonna ask about example R5.
In R5 there is (2,3)
2<=3 but 3 is not <=2
What would be the other info to check that R5 is antisymmetric?
• Mar 1st 2010, 02:22 AM
PiperAlpha167
Quote:

Originally Posted by JazzGuitarist01
I am having a little trouble wrapping my head around this. I understand
the Reflexive, Symmetric, and Transitive properties just fine but do not understand the Antisymmetric examples my textbook gives.

Consider the following relations on {1,2,3,4}

R5={(1,1),(1,2),(1,3),(1,4),(2,2),(2,3),(2,4),(3,3 ),(3,4),(4,4)}
R6={(3,4)}

If anybody could help explain why the above satisfy the Antisymmetric property I would really appreciate it.

R6 is vacuously antisymmetric, because the matrix of the statement defining the property is a material conditional, and the antecedent can not be satisfied.

You can show that R5 is antisymmetric by simply considering all those cases where the antecedent is satisfied,
and establishing that the consequent is also satisfied.

You can just grind it out, if you like.
E.g., if (1,1) in R5 and (1,1) in R5, then (1,1) in R5. ... .