Dad's List

As you may know, Joseph keeps a food list. It can have only three things he will not eat. If I serve something on the list, he gets to eat something else for dinner. If it's not on the list and I serve it, he can eat it or not, but he doesn't get anything else. Any changes to the list go into effect the next day.
He came into the kitchen to check on the acceptability of the food I was cooking.
Suspicious.
So, he asked "Does it have tomatoes in it?"
"Not yet. Are tomatoes on your list?"
"No."
"There, now it has tomatoes."

But he didn't know what thing to take off to put tomatoes on. He solved that one by making a list for Dave.

Dave saw his list a couple days later. "Is this his way of extending his list?"
"Yup!"

You'll notice, this list has a couple of Dave's favorite foods!