procedure RZEXTR(IEST:integer; XEST:real; YEST:array of real;
                           var YZ, DY:array of real; NV, NUSE:integer);
var
    FX:array[0..7] of real;   J,M1,K:integer;
    YY,V,C,B1,DDY,B:real;
begin
    SetLength(D, 11, 8);
    X[IEST]:=XEST;
    If IEST = 1 Then
    begin
        For J:=1 To NV do
        begin
            YZ[J]:=YEST[J];
            D[J, 1]:=YEST[J];
            DY[J]:=YEST[J];
        end;
    end 
    Else
    begin
        M1:=IEST;
        If NUSE < IEST Then M1:=NUSE;
        For K:=1 To M1 - 1 do
            FX[K + 1]:=X[IEST - K] / XEST;
        For J:=1 To NV do
        begin
            YY:=YEST[J];
            V:=D[J, 1];
            C:=YY;
            D[J, 1]:=YY;
            For K:=2 To M1 do
            begin
                B1:=FX[K] * V;
                B:=B1 - C;
                If B <> 0 Then
                begin
                    B:=(C - V) / B;
                    DDY:=C * B;
                    C:=B1 * B;
                end
                Else
                    DDY:=V;
                If K <> M1 Then V:=D[J, K];
                D[J, K]:=DDY;
                YY:=YY + DDY;
            end; 
            DY[J]:=DDY;
            YZ[J]:=YY;
        end; 
    end;
end;