EXTERNAL

SUB zbrak (dum, x1, x2, n, xb1(), xb2(), nb)

    DECLARE FUNCTION func         ! Supplied by the user

    LET nbb = nb
    LET nb = 0
    LET x = x1
    LET dx = (x2 - x1) / n
    LET fp = func(x)
    FOR i = 1 to n
        LET x = x + dx
        LET fc = func(x)
        IF fc * fp < 0 then
           LET nb = nb + 1
           LET xb1(nb) = x - dx
           LET xb2(nb) = x
        END IF
        LET fp = fc
        IF nbb = nb then EXIT SUB
    NEXT i

END SUB