Here we make available a preprint of "Efficient, Verified Checking of Propositional Proofs" by Marijn Heule, Warren Hunt, Jr., Matt Kaufmann, and Nathan Wetzler.
Here are slides presented at ITP 2017.
NOTE: The paper mentions a related, independent proof development in Coq. The final version of the paper will also mention a recent related, proof development in Isabelle by Peter Lammich.