Kosheir (Tying a Permanent Knot) - Breaking Down the 39 Melachot

Your garbage bag is full on Shabbat and  you want to tie up the top to take it   outside so that it doesn't spill. Are you  allowed to take the whole top of the bag,   twist it and make a single knot?Or, are  you allowed to take the two ends and tie   a double knot? The same question is if you  have shoelaces that keep becoming undone. Are   you allowed to tie a double knot on top so that  they don't become undone on Shabbat? And lastly,   are you allowed to make a necktie on Shabbat?  The kind of necktie that's an actual knot,   not the kind that when you remove one side,  the whole thing unravels. The answer is one of   the melachot of Shabas is the melacha of Kosheir,  which means tying a permanent knot. And therefore,   you are not allowed to take the top of the garbage  bag and simply make one big knot at the top. You   cannot take the two ends of a garbage bag and  tie a double knot. You cannot tie a double knot   on your shoes on Shabbat. And you cannot make  a necktie, even if you're going to take it out   afterwards, if it's the kind that does not  unravel when you pull out one of the ends.