How do you get back to pewter city from cerulean city?

How do you get back to pewter city from cerulean city?
You can get back to Pewter City with the HM Fly. You get fly if you go to Celadon City, and go to the farthest left. (Make sure you have a Pokemon with the move Cut.) Go out of the city, and go up, and cut down the tree. Pass through the double building, and when you get outside, there should be a house. Go into and a girl will give you the HM to keep her house a secret. Now, you can fly back to Pewter City! June Days