The setup for the next exercise has both fencers in Secunda. As your opponent thrusts, you’ll trace a counter-clockwise circle with your point such that you push his blade to your outside with the true edge.
From here you may be inclined to simply raise your point and thrust. And that can work if the opponent is slow, but if he is quick he may try to parry you in the same manner that you parried him.
So instead you are instructed to “riposte him in Quarta above over his arm”. Given the acompanying illustration, I interpret this to mean that you trace a clockwise circle with your tip, thrusting once you reach Quarta on the inside.
Now your opponent needs to push your blade to the right past the entire breadth of his body. And this must be done with the weaker false edge.
Note: L’Ange warns us to use the off-hand to parry any counter-thrust at this time. However, this is not shown in the illustration.