Question

My question is who has written the bed purana and all the granthas

Answer 1

Ganesha imposes a precondition that he would do so only if Vyasa would narrate the story without a pause. Vyasa set a counter-condition that Ganesha understand the verses first before transcribing them. Thus Vyasa narrated the entire Mahābhārata and all the Upanishads and the 18 Puranas, while Lord Ganesha wrote.