It's missing the usual use of the verb 'use'.
"This knife is used to cut meat."
Yes. I think the reason it isn't on that diagram is that is not really an idiomatic "used to" structure. It's the verb "used" following by a prepositional phrase beginning with "to". But if you're teaching "used to", you might as well point it out to avoid confusion.So I can use your point when teaching.
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