Working group 1 summary: $V_{ud}$, $V_{us}$, $V_{cd}$, $V_{cs}$ and semileptonic/leptonic $D$ decays

We summarize the program of working group 1 at the 12th Workshop on the CKM Unitarity Triangle, whose main subjects covered $V_{ud}$, $V_{us}$, and first-row unitarity as well as $V_{cd}$, $V_{cs}$, and (semi-)leptonic $D$ decays.