What should one do who, having fallen behind the Imam, did not bow with him, then realized it while the Imam was prostrating?

If a follower (ma'mum) makes a mistake and the Imam precedes him by two actual pillars, he must perform them and follow his Imam. If the Imam precedes him by three intended pillars (excluding standing after bowing and sitting between the two prostrations), the most correct view is that he should join his Imam and perform an additional raka'ah after the Imam's salutations. So, if someone becomes aware while standing and his Imam is prostrating, he must perform what he missed and follow his Imam, unless the Imam has risen from the second prostration before he catches up. In that case, he should abandon catching up, join his Imam, and perform an additional raka'ah after the salutations.