Happy seL4 day! On July 29, 2009, the last "sorry" of the seL4 functional correctness proof was eliminated. A "sorry" is an assumed theorem lacking a complete proof. "0 sorries" meant there was nothing left to prove: the project was finished. We now celebrate this day every year to mark the seL4 day, when the world's first formally verified kernel with a machine-checked code-level proof came into existence. In July 2014, on the 29th to make the "seL4 day" a double-celebratory day, the seL4 code and proofs became open source, paving the way to the widespread use [0] it enjoys today. A big thank-you to all for your continued support! Learn more about the history of seL4 [1]. [0] https://sel4.systems/use.html [1] https://sel4.systems/About/history.html Birgit Brecknell seL4 Foundation Project Coordinator Sydney, Australia Mon 9-5 Wed 2-5 Fri 9-5 birgit@sel4.systems <mailto:birgit@sel4.systems> bbrcknl@gmail.com <mailto:bbrcknl@gmail.com>