using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;

// (づ°ω°)づﾐe★゜・。。・゜゜・。。・゜☆゜・。。・゜゜・。。・゜
public class Solver
{
    private const int MOD = 1000000007;

    long ModPow(long x, long p)
    {
        long ret = 1;
        while (p > 0)
        {
            if ((p & 1) == 1)
                ret = ret * x % MOD;
            x = x * x % MOD;
            p >>= 1;
        }
        return ret;
    }

    long[] f, rf, inv;
    void InitFacts(int size)
    {
        f = new long[size + 1];
        rf = new long[size + 1];
        inv = new long[size + 1];
        f[0] = f[1] = rf[0] = rf[1] = inv[1] = 1;
        for (int i = 2; i <= size; i++)
        {
            f[i] = f[i - 1] * i % MOD;
            inv[i] = inv[MOD % i] * (MOD - MOD / i) % MOD;
            rf[i] = inv[i] * rf[i - 1] % MOD;
        }
    }

    const int MAX = 2000;

    public void Solve()
    {
        int n = ReadInt();
        var a = ReadIntMatrix(n);

        var dp = new int[2 * MAX + 1, 2 * MAX + 1];
        for (int i = 0; i < n; i++)
            dp[MAX - a[i][0], MAX - a[i][1]]++;

        for (int i = 0; i <= 2 * MAX; i++)
            for (int j = 0; j <= 2 * MAX; j++)
            {
                if (i < 2 * MAX)
                    dp[i + 1, j] = (dp[i + 1, j] + dp[i, j]) % MOD;
                if (j < 2 * MAX)
                    dp[i, j + 1] = (dp[i, j + 1] + dp[i, j]) % MOD;
            }

        long ans = 0;
        for (int i = 0; i < n; i++)
            ans += dp[MAX + a[i][0], MAX + a[i][1]];

        InitFacts(4 * MAX + 1);
        for (int i = 0; i < n; i++)
            ans -= f[a[i][0] * 2 + a[i][1] * 2] * rf[a[i][0] * 2] % MOD * rf[a[i][1] * 2] % MOD;

        ans %= MOD;
        ans += MOD;

        Write(ans * inv[2] % MOD);
    }

    #region Main

    protected static TextReader reader;
    protected static TextWriter writer;
    static void Main()
    {
#if DEBUG
        reader = new StreamReader("..\\..\\input.txt");
        //reader = new StreamReader(Console.OpenStandardInput());
        writer = Console.Out;
        //writer = new StreamWriter("..\\..\\output.txt");
#else
        reader = new StreamReader(Console.OpenStandardInput());
        writer = new StreamWriter(Console.OpenStandardOutput());
        //reader = new StreamReader("input.txt");
        //writer = new StreamWriter("output.txt");
#endif
        try
        {
            new Solver().Solve();
            //var thread = new Thread(new Solver().Solve, 1024 * 1024 * 128);
            //thread.Start();
            //thread.Join();
        }
        catch (Exception ex)
        {
#if DEBUG
            Console.WriteLine(ex);
#else
            throw;
#endif
        }
        reader.Close();
        writer.Close();
    }

    #endregion

    #region Read / Write
    private static Queue<string> currentLineTokens = new Queue<string>();
    private static string[] ReadAndSplitLine() { return reader.ReadLine().Split(new[] { ' ', '\t', }, StringSplitOptions.RemoveEmptyEntries); }
    public static string ReadToken() { while (currentLineTokens.Count == 0)currentLineTokens = new Queue<string>(ReadAndSplitLine()); return currentLineTokens.Dequeue(); }
    public static int ReadInt() { return int.Parse(ReadToken()); }
    public static long ReadLong() { return long.Parse(ReadToken()); }
    public static double ReadDouble() { return double.Parse(ReadToken(), CultureInfo.InvariantCulture); }
    public static int[] ReadIntArray() { return ReadAndSplitLine().Select(int.Parse).ToArray(); }
    public static long[] ReadLongArray() { return ReadAndSplitLine().Select(long.Parse).ToArray(); }
    public static double[] ReadDoubleArray() { return ReadAndSplitLine().Select(s => double.Parse(s, CultureInfo.InvariantCulture)).ToArray(); }
    public static int[][] ReadIntMatrix(int numberOfRows) { int[][] matrix = new int[numberOfRows][]; for (int i = 0; i < numberOfRows; i++)matrix[i] = ReadIntArray(); return matrix; }
    public static int[][] ReadAndTransposeIntMatrix(int numberOfRows)
    {
        int[][] matrix = ReadIntMatrix(numberOfRows); int[][] ret = new int[matrix[0].Length][];
        for (int i = 0; i < ret.Length; i++) { ret[i] = new int[numberOfRows]; for (int j = 0; j < numberOfRows; j++)ret[i][j] = matrix[j][i]; } return ret;
    }
    public static string[] ReadLines(int quantity) { string[] lines = new string[quantity]; for (int i = 0; i < quantity; i++)lines[i] = reader.ReadLine().Trim(); return lines; }
    public static void WriteArray<T>(IEnumerable<T> array) { writer.WriteLine(string.Join(" ", array)); }
    public static void Write(params object[] array) { WriteArray(array); }
    public static void WriteLines<T>(IEnumerable<T> array) { foreach (var a in array)writer.WriteLine(a); }
    private class SDictionary<TKey, TValue> : Dictionary<TKey, TValue>
    {
        public new TValue this[TKey key]
        {
            get { return ContainsKey(key) ? base[key] : default(TValue); }
            set { base[key] = value; }
        }
    }
    private static T[] Init<T>(int size) where T : new() { var ret = new T[size]; for (int i = 0; i < size; i++)ret[i] = new T(); return ret; }
    #endregion
}

Measured memory_bytes: 79312