public static Fraction det( Fraction m[][] )
	{
		int countSwap = 0;

		for( int i = 0; i < m.length; i++ )
		{
			if( m[i][i].equals( 0 ) )
				for( int j = i + 1; j < m[i].length; j++ )
					if( !m[j][i].equals( 0 ) )
					{
						m = swapLine( j, i, m );
						countSwap++;
						break;
					}

			for( int j = i; j < m.length; j++ )
			{
		 		if( i != j )
				{
					Fraction addFra = m[i][i].inv( ).mult( new Fraction( -1 ) ).mult( m[j][i] );
					if( addFra.getDenominator( ) == 0 )
						return null;
					m = addLine( i, j, addFra, m );
				}
			}
		}

		Fraction ret = new Fraction( 1 );

		for( int k = 0; k < m.length; k++ )
			ret = ret.mult( m[k][k] );

		if( countSwap % 2 != 0 )
			ret = ret.mult( new Fraction( -1 ) );

		return ret;
	}