Get Your Prox Off

Create a triangle. Find a point somewhere inside it. Choose a corner at random and move halfway towards it. Mark the new point. Repeat the procedure: choose, move, mark. Repeat again and again. In time, a fractal will appear:


However, if you try the same thing with a square – choose a corner at random, move halfway towards it, mark the new point, repeat – no fractal appears. Instead, the points fill the interior of the square:


But what happens if you impose restrictions on the randomly chosen corner (or chorner)? Suppose you can’t choose the same corner twice in a row. If this rule is applied to the square, this fractal appears:



Now apply the no-corner-twice-in-a-row rule to a square that contains a central chorner. This fractal appears:


And if the rule is that you can choose a corner twice in a row but not thrice? This fractal appears:



Here is the rule is that a corner can’t be chosen if it was chosen two moves ago:


But what if the restriction is based not on how often or when a corner is chosen, but on its proximity, i.e. how near it is to the marked point? If the nearest corner can’t be chosen, the result is the same as the no-corner-twice-in-a-row rule:


But if the second-nearest corner can’t be chosen, this fractal appears:


This is the fractal when the third-nearest corner can’t be chosen:


And this is the fractal when the fourth-nearest, or most distant, corner can’t be chosen:


Here are the same restrictions applied to a pentagon:


Nearest corner forbidden


Second-nearest corner forbidden


Third corner forbidden


Fourth corner forbidden


Fifth corner forbidden


Fifth corner forbidden (animated)

And a pentagon with a central chorner:


Now try excluding more than one corner. Here are pentagons excluding the n-nearest and n+1-nearest corners (for example, the nearest and second-nearest corners; the second-nearest and third-nearest; and so on):


But what if the moving point is set equal to the n-nearest corner before it moves again? If the corner is the second-nearest and the shape is a triangle with a central chorner, this is the fractal that appears:



Animated version

And here is the same rule applied to various n-nearest corners in a pentagon:


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