Proof

 is the fourth chapter of Attack on Titan: No Regrets, written by Gun Snark and illustrated by Hikaru Suruga.

Summary
As Levi, Farlan Church, and Isabel Magnolia get their first glimpse of the world outside the Walls, they are amazed at the beauty and freedom. But not long after their departure a Titan is sighted. The Survey Corps jumps into action working in unison to try and take out the Titan. At the same time a Deviant Type Titan appears. With the formation beginning to fail, it's up to Levi's squad to get rid of the new threat. Together they make easy work of the Titan. While Erwin Smith marvels at their accomplishment, satisfied that he made the right decision.