A model writes one word at a time after a prompt. Every word in the text, the prompt’s and each one the model writes, needs a key and a value worked out once it’s in the text: that’s what later words listen to in “Listen and collect”. Write work_to_write(prompt_length, new_words): how many words’ keys and values it has to work out to write new_words words after the prompt, if it never works anything out twice.