%!PS

/fibseq {
    1 1 f
} bind def

/f {
    3 dict begin
    /z exch def
    /y exch def
    /x exch def
    x y lt {
        x 0 eq {
            1
        } {
            0
        } ifelse
    } {
        x y sub y z add y f
        x y z add y f
        add
    } ifelse
    end
} bind def

16 fibseq 4 eq { (Pass) } { (FAIL) } ifelse print ( ) print
9 fibseq 2 eq { (Pass) } { (FAIL) } ifelse print ( ) print
15 fibseq 2 eq { (Pass) } { (FAIL) } ifelse =