unordered(x,y) returns the value 1 (true) if x, y, or both are a
    NaN and returns the value 0 (false) otherwise.

                           Entry-Point Names

    Generic
    Function   Data Type   OpenVMS                Tru64 UNIX
    Name       Required

    unordered  S_FLOAT     math$unordered_s       unorderedf
               T_FLOAT     math$unordered_t       unordered
               X_FLOAT     math$unordered_x       unorderedl
               F_FLOAT     math$unordered_f
               G_FLOAT     math$unordered_g