Do it formally.
Don't agree to "send over a demo" unless you have a full product you can lock down. If there's an interest, arrange a personal demonstration. If they decide that's too much formality, you don't want to be working for them, trust me.
"There's a set of rules that anything that was in the world when you were born is normal and natural. Anything invented between when you were 15 and 35 is new and revolutionary and exciting, and you'll probably get a career in it. Anything invented after you're 35 is against the natural order of things."
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