Let $A$ be a graded quadratic algebra over a field $k$, and suppose that it admits the Koszul dual $A^!$. I want to know if there is a natural pairing $A\otimes A^!\to k$ or something similar to this. I found a vague statement on this line at the beginning of Section 1.4 of this note by Yanki Lekili, but there are no references there and I couldn't find any.
I'm also interested in operads, and I welcome any analogous statement in operadic setting (my original motivation is coming from there).
Thank you.