checking whether the number is NaN

[Red]

>
>> Tell me please,are there any way to check whether number is 
>> NaN?
>
> http://dlang.org/phobos/std_math.html#isNaN
>


pure nothrow @trusted bool isNaN(real x);

Returns !=0 if e is a NaN.

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Seems like a slight documentation disagreement. Shows bool 
prototype but description says returns !=0