The standard requires that you can compare any two floating point numbers, as long as they share the same radix.
The unordered condition arises when at least one operand is NaN.
Note that \(x\ne x\) returns true for \(x=\NaN\). This is often used to check if a result is NaN.
Be careful in equating \(x\le y\) with the negation of \(x>y\). When one of the operands is NaN, then the former returns False, as does the latter.
Note: \(+0=-0\) is always true.