input: Write a function to explain how recursion works in Python. The function should describe recursion as a technique to solve problems by defining them in terms of themselves and breaking them down into smaller problems until a base case is reached. The function should also mention that a recursive function in Python is one that calls itself.
  assert explain_recursion()=="""Recursion is a powerful technique for solving problems. It involves defining a problem in terms of itself. A recursion problem is solved by breaking it down into smaller problems, until the problem is small enough to be solved directly. The result from a smaller problem can then be combined with the result from the larger problem, until the original problem is solved. In Python, a recursive function is one that calls itself."""
output: def explain_recursion():
      return "Recursion is a powerful technique for solving problems. It involves defining a problem in terms of itself. A recursion problem is solved by breaking it down into smaller problems, until the problem is small enough to be solved directly. The result from a smaller problem can then be combined with the result from the larger problem, until the original problem is solved. In Python, a recursive function is one that calls itself."