+1  A: 

I don't think it's quite right - what you are saying in your formula is that there exists a z such that z is either less than x or y is less than z, which is different then the sentence you described.

I think what you want is more

Ax Ey s.t. not (E z) with x < z < y

James Kingsbery  2010-06-09 14:48:30
+1  A: 

I think you need to address the word "unique" so you need something in there along the lines of ^(z!=x!=y) the "^" meaning AND.

However, I'm not sure you need the Y. I think it would be sufficient to say

(Ax)(Ez) [(L(x,z) v L(z,x)) ^ (NOT)(x=z)]

I'm still not sure if this is the best way to say it, but just make sure what you write, reads exactly how you want it to. Hope this helps!

Elaina R  2010-06-09 14:50:25
Hi,I am NOT allowed to use (x=z) equivalency testing. My solutionwould have been what you suggested if (x=y) testing were to be allowed.
none  2010-06-09 15:59:07
A suggested solution from a classmate...Ax Ey [L(x,y) and neg Ez(L(z,y) and L(x,z))]
none  2010-06-09 16:07:47
Oh, then that is more difficult. I agree with your classmate, that solution does make sense
Elaina R  2010-06-09 17:04:29

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