A 2-glider collision is the collision, at right angles or head-on, of two gliders. The gliders can react with each other in many different ways; a large number of the reactions cleanly destroy both gliders leaving nothing. Many of the remaining reactions cleanly create some common objects, and so are used as the first steps in glider synthesis or as part of constructing interesting objects using rakes. Only a small number of collisions can be considered dirty due to creating multiple objects or a mess.
Here is a list of the possible results along with how many different ways they can occur (ignoring reflections and rotations).
|Lumps of muck||1||0|
|Four skewed blocks||0||1|
The messiest of the two-glider collisions in the "dirty" category is 2-glider mess.