L = (N2-N1+1)/2+N1
	IR = N2

 10	if (L .gt. N1) then
	    L = L-1
	    RRA = RA(L)
	    RRB = RB(L)
	else
	    RRA = RA(IR)
	    RRB = RB(IR)
	    RA(IR) = RA(N1)
	    RB(IR) = RB(N1)
	    IR = max(N1,IR-1)	! 'max' needed to sort one element (N1=N2)
	    if (IR .eq. N1) then
		RA(N1) = RRA
		RB(N1) = RRB
		return
	    end if
	end if

	I = L
	J = L+L-N1+1

	do while (J .le. IR)
	    if (J .lt. IR) then
		if (RA(J) .lt. RA(J+1)) J=J+1
	    end if
	    if (RRA .lt. RA(J)) then
		RA(I) = RA(J)
		RB(I) = RB(J)
		I = J
		J = J+J-N1+1
	    else
		J = IR+1
	    end if
	end do

	RA(I) = RRA
	RB(I) = RRB

	go to 10