In Crumble, it is not generally possible to continually threaten to occupy the same piece. Typically the resources that are local to the battle for any given piece will be exhausted because the split piece is often the wrong shape to split and swap again in the same direction.

In the above example, Black and White both wanted to occupy the same piece, but they each had limited resources to do it. After those resources were used up, the battle was over and the target piece couldn't be occupied again. An important skill in the game of Crumble is to be able to calculate the result of this sort of battle.

But in some cases, one player is guaranteed to have enough resources to keep fighting for the same piece; or both players are, in which case they may risk invoking the 'draw rule' if neither side can afford to back down.

These guaranteed resources are called 'renewables'. There are two known forms of renewables in Crumble. One is called a 'whip' and the other is called a 'gun'. Renewables are very powerful. If two people are playing Crumble, and one of them knows about renewables while the other doesn't, the one who knows about renewables will crush the other player.

The Whip

This is the simplest form of renewable. If two pieces share the characteristic of being both splittable and swappable, they form a renewable.

To use a whip, simply perform a long split through both pieces, and swap as normal. Consider the example from above, this time where Black has a renewable.

Black can keep this up indefinitely, creating a new, smaller renewable to replace the old as part of each turn. Each time a player does this, it is called 'iterating the renewable', or simply 'iterating'.

The Gun

This is a more complicated form of renewable, and tends to occur later in the game. It accomplishes nearly the identical result as the whip; the main difference being that the whip must give up a smaller and smaller amount of material with each iteration, while the gun gives up nothing at all.

The target piece is occupied, and the gun has resumed its original shape. It can keep iterating between split/swap/captures and join/swap/captures indefinitely.

Assessing A Renewable

A renewable can be strong or weak. A weak renewable is one that has nothing to swap into - it either doesn't border a swappable region of pieces, or the swappable pieces it does border are not significant.

A strong renewable is one that can swap into something useful. Either it borders a large region of swappable pieces that can be occupied one by one until the material advantage chokes out the opponent, or it borders a key piece as in the above diagrammed examples.

One of the first things a beginning Crumble player should do is learn to recognize renewables when they appear. The whip is extremely common, and each occurrence must be evaluated, and if necessary, broken.

The True Value Of Renewables

When playing against a player who also understands renewables, you'll find that their true strength lies in the single turn you force the opponent to expend in breaking them.

Renewables are fragile - it only takes one turn to break one - but in a pitched battle, that may not be a move your opponent can afford to waste. If you create a strong renewable and use it to occupy a crucial piece, you may only need one more move yourself to safeguard that piece and ensure that it will remain yours for the longer term - or perhaps become impervious to any future occupation. In that case, your opponent can only continue the battle over that piece by first breaking your renewable. Very often, this is a sign that they have lost that battle, and must turn their attention to others on the board that they might win.

Sometimes a renewable is so strong that it can occupy a piece that is absolutely crucial to the position. We call such a piece a 'linchpin'. Typically it's a piece that, if you were allowed to occupy and retain it for more than one move, you'd be able to win on the next move or do a devastating capture. In that case, the opponent may not have the time to break your renewable, and therefore finds themselves with only non-renewable resources available to re-occupy that piece.

In that case, it would not be unusual for that player to resign the game at once. A renewable can be so strong that its mere existence is enough to win the game outright.

How To Break A Renewable

Renewables are very fragile. The best way is to split their entry-point into your swappable region. If you can then gain a little material by swapping the newly split piece, that's a bonus.

The renewable is broken; the target piece is safe. But be careful. Sometimes you might think you're breaking a renewable, but it turns out there's another renewable in the same location that you didn't count on.

White broke Black's renewable, but there was another one right there to take up the slack. That's a particular danger to watch out for when breaking whips.

A gun can be broken by occupying any piece that's an integral part of the gun.

Black's gun has been broken. The target piece is safe - at least, safe from that renewable.

When To Break A Renewable

Almost always, do this immediately. If you see that your opponent has created a renewable - even if they have not yet iterated it - and if you see that their renewable is strong, then there is virtually no benefit to waiting. Destroy it now. If you wait, you leave the opponent free to use it, and then you may have to break it, probably under worse circumstances.

A weak renewable can be left alone, and this is why it's important to be able to identify and assess renewables as they appear on the board: a weak one doesn't matter, while a strong one must be broken as soon as it appears.

Very rarely, there may be a benefit to letting a whip iterate a few times before breaking it. This is because each iteration of a whip converts a small amount of the opponent's material to your color. If those little pieces will connect one of your chains in a strategically significant way, then the threat of giving you that connection may be enough to prevent the opponent from iterating that renewable. Or, if one of those little pieces could be split and swapped someplace strategically significant, then that likewise might be enough of a threat to prevent them from iterating their renewable. But these situations require fine judgment.

White waited until Black's renewable produced a piece White could use to occupy another target piece.

A 'Draw Turn'

When either player iterates a renewable to swap into a piece, and the other player immediately iterates a renewable to swap into the same piece, and if no captures (other than the capture intrinsic to a gun, if a gun form of renewable is used) are performed by either player, we call this a 'draw turn'.

The above two moves (one by Black and one by White) constitute a single ‘draw turn’.

Note that it doesn't matter how many pieces are involved in the swap. It also doesn't matter whether the players use whips, guns, or an as-yet undiscovered type of renewable. What defines a draw turn is that both sides use renewables, both sides occupy the same piece, and no captures occur.

Draw turns are important to understand, because Crumble's draw rule (the equivalent to three-fold repetition in chess) states that if there are three draw turns in a row, even if the target piece is different in each draw turn, the game is declared a draw.

The Bigger Picture

Crumble uses simple squares and half-squares for pieces, with simple rules governing how they behave. But because the rules allow pieces to act together to perform long splits, big joins, long swaps, and captures, it's possible for clusters of pieces to develop abilities that none of them would have had on their own.

In this way it becomes possible to play for positions where big, important moves become available, like pins and knight forks in chess, that when used together produce elegant forcing maneuvers. In Crumble, these types of combinations can be used to break through your opponent's position, revealing that what may have seemed to be an impervious chain of pieces, was really exposed and weak.

The variety and depth of attacking conceptions in Crumble matches the spirit found in chess. But in chess there is only one king to mate, while in Crumble, each battle contains its own checkmate, for one player or the other, and each may involve the full range of tactical and strategic possibilities in the game, in whichever isolated corner of the playing field they occur.