CRDT operation design

# collaborative todo list class TodoList: def __init__(self): self.items = [] def add(self, name): self.items.append(name) def remove(self, name): if name in self.items: self.items.remove(name) # two replicas: A adds 'x' then removes 'x'; B concurrently adds 'x' A plain list with append/remove does not converge across replicas. Which change makes the structure a proper CRDT?