Burn
A burn is a reaction which travels indefinitely as a wave through the components of a wick or an agar. A burning wick is known as a fuse.
If the object being burned has a spatial periodocity, then the active area of the burning usually remains bounded and so eventually develops a periodicity too. It is unknown whether this will always occur.
The speed of burning can range from arbitrarily slow up to the speed of light. The results of burning can be clean (leaving no debris), or leaving debris usually much different from the original object. In rare cases, a reburnable fuse produces an exact copy of the original object, allowing the creation of objects such as the telegraph.
In many useful cases burning can be initiated by impacting an object with gliders or other spaceships. An object might be able to burn in more than one way, depending on how the burn is initiated.