input: Write a function to create a web application in Python using Flask that will take user input and generate an HTML page with the input. The function should define the Flask application, the home route that handles both GET and POST requests, and the HTML templates for the index and result pages.
  
  assert create_flask_app() is not None
output: def create_flask_app():
      from flask import Flask, request, render_template
  
      app = Flask(__name__)
  
      @app.route('/', methods=['GET', 'POST'])
      def home():
          if request.method == 'POST':
              user_input = request.form['user_input']
              return render_template('result.html', user_input=user_input)
          return render_template('index.html')
  
      return app