Hi(adsbygoogle = window.adsbygoogle || []).push({});

I was reading through a textbook and I came across the set theoretic definition of an ordered pair (Kuratowski), where (x,y)={{x},{x,y}}, which apparently can be shortened to {x,{x,y}}. This seems to be the standard definition for an ordered pair in set theory so that we can determine both the first and second element using only set theory and no notions of "first" or "second". However, I am wondering why the less complicated definition (x,y)={x,{y}} does not also work.

Can anyone enlighten me?

**Physics Forums | Science Articles, Homework Help, Discussion**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Question about set theory and ordered pairs

**Physics Forums | Science Articles, Homework Help, Discussion**