The second step follows from the recursive definition of .
Another example is the recursive definition of a process tree:
It is possible, though difficult, to create a recursive definition of multiplication with set theory.
For example, the following is a recursive definition of a person's ancestors:
For this reason recursive definitions are very rare in everyday situations.
This is done by using a recursive definition similar to the syntax.
We use a recursive definition, and do so on the stack.
One approach, roughly speaking, is to consider the collection of all domains as a domain itself, and then solve the recursive definition there.
It is chiefly in logic or computer programming that recursive definitions are found.
This is precisely the recursive definition of 0 and S.