Task: 4-rings or 4-squares puzzle
C#: using System;
using System.Linq;

namespace Four_Squares_Puzzle {
    class Program {
        static void Main(string[] args) {
            fourSquare(1, 7, true, true);
            fourSquare(3, 9, true, true);
            fourSquare(0, 9, false, false);
        }

        private static void fourSquare(int low, int high, bool unique, bool print) {
            int count = 0;

            if (print) {
                Console.WriteLine("a b c d e f g");
            }
            for (int a = low; a <= high; ++a) {
                for (int b = low; b <= high; ++b) {
                    if (notValid(unique, b, a)) continue;

                    int fp = a + b;
                    for (int c = low; c <= high; ++c) {
                        if (notValid(unique, c, b, a)) continue;
                        for (int d = low; d <= high; ++d) {
                            if (notValid(unique, d, c, b, a)) continue;
                            if (fp != b + c + d) continue;

                            for (int e = low; e <= high; ++e) {
                                if (notValid(unique, e, d, c, b, a)) continue;
                                for (int f = low; f <= high; ++f) {
                                    if (notValid(unique, f, e, d, c, b, a)) continue;
                                    if (fp != d + e + f) continue;

                                    for (int g = low; g <= high; ++g) {
                                        if (notValid(unique, g, f, e, d, c, b, a)) continue;
                                        if (fp != f + g) continue;

                                        ++count;
                                        if (print) {
                                            Console.WriteLine("{0} {1} {2} {3} {4} {5} {6}", a, b, c, d, e, f, g);
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }
            if (unique) {
                Console.WriteLine("There are {0} unique solutions in [{1}, {2}]", count, low, high);
            }
            else {
                Console.WriteLine("There are {0} non-unique solutions in [{1}, {2}]", count, low, high);
            }
        }

        private static bool notValid(bool unique, int needle, params int[] haystack) {
            return unique && haystack.Any(p => p == needle);
        }
    }
}

VB: Dim a As Integer, b As Integer, c As Integer, d As Integer
Dim e As Integer, f As Integer, g As Integer
Dim lo As Integer, hi As Integer, unique As Boolean, show As Boolean
Dim solutions As Integer
Private Sub bf()
    For f = lo To hi
        If ((Not unique) Or _
            ((f <> a And f <> c And f <> d And f <> g And f <> e))) Then
            b = e + f - c
            If ((b >= lo) And (b <= hi) And _
                ((Not unique) Or ((b <> a) And (b <> c) And _
                (b <> d) And (b <> g) And (b <> e) And (b <> f)))) Then
                solutions = solutions + 1
                If show Then Debug.Print a; b; c; d; e; f; g
            End If
        End If
    Next
End Sub
Private Sub ge()
    For e = lo To hi
        If ((Not unique) Or ((e <> a) And (e <> c) And (e <> d))) Then
            g = d + e
            If ((g >= lo) And (g <= hi) And _
                ((Not unique) Or ((g <> a) And (g <> c) And _
                (g <> d) And (g <> e)))) Then
                bf
            End If
        End If
    Next
End Sub
Private Sub acd()
    For c = lo To hi
        For d = lo To hi
            If ((Not unique) Or (c <> d)) Then
                a = c + d
                If ((a >= lo) And (a <= hi) And _
                    ((Not unique) Or ((c <> 0) And (d <> 0)))) Then
                    ge
                End If
            End If
        Next d
    Next c
End Sub
Private Sub foursquares(plo As Integer, phi As Integer, punique As Boolean, pshow As Boolean)
    lo = plo
    hi = phi
    unique = punique
    show = pshow
    solutions = 0
    acd
    Debug.Print
    If unique Then
        Debug.Print solutions; " unique solutions in"; lo; "to"; hi
    Else
        Debug.Print solutions; " non-unique solutions in"; lo; "to"; hi
    End If
End Sub
Public Sub program()
    Call foursquares(1, 7, True, True)
    Debug.Print
    Call foursquares(3, 9, True, True)
    Call foursquares(0, 9, False, False)
End Sub