Strict weak ordering implies ordering is not defined for all elements?

[JUAN DENT]

Hi,

I have found in http://sidd-reddy.blogspot.be/2011/01/i-was-going-over-c-stl-when-i-noticed.html that strict weak ordering implies incomparability, i.e. that for an ordering function cmp, there exists elements in its domain where neither cmp(a,b) nor cmp(b,a) are true.

What kind of function could behave like this? Some example anyone?

Thanks,
Juan

[Peter87]

there exists elements in its domain where neither cmp(a,b) nor cmp(b,a) are true.

With strict weak ordering that only happens when a is considered equal to b.