input: Write a function to explain how recursion can be used to solve a given problem in Python. The function should provide a concise explanation of recursion, how it works, and its use in solving problems by breaking them down into smaller subproblems and combining their results. The function should also include an example of a simple recursive problem, such as calculating the factorial of a number.
  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. For example, calculating the factorial of a number involves multiplying the number by the factorial of the number minus one, until the base case of 0 or 1 factorial is reached, which is 1.\"""
  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. For example, calculating the factorial of a number involves multiplying the number by the factorial of the number minus one, until the base case of 0 or 1 factorial is reached, which is 1.\"""
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. For example, calculating the factorial of a number involves multiplying the number by the factorial of the number minus one, until the base case of 0 or 1 factorial is reached, which is 1."""