term% ls -F
term% cat index.txt
NAN(2)                        System Calls Manual                       NAN(2)

       NaN, Inf, isNaN, isInf - not-a-number and infinity functions

       #include <u.h>
       #include <libc.h>

       double NaN(void)

       long   Inf(int)

       int    isNaN(double)

       int    isInf(double, int)

       The  IEEE  floating point standard defines values called `not-a-number'
       and positive and negative `infinity'.  These values can be produced  by
       such  things as overflow and division by zero.  Also, the library func‐
       tions sometimes return them when the arguments are not in  the  domain,
       or the result is out of range.

       NaN  returns  a double that is not-a-number.  IsNaN returns true if its
       argument is not-a-number.

       Inf(i) returns positive infinity if i is greater than or equal to zero,
       else  negative  infinity.   IsInf returns true if its first argument is
       infinity with the same sign as the second argument.