The article in question
contains an important result on the behavior of the Hardy–Littlewood maximal
function MSn on the unit n-sphere, providing a weak-type linear bound that has not
been improved on in the intervening decades. Unfortunately, the proof has a gap,
since it relies on an incorrect intermediate result (Lemma 3). We correct the proof by
providing a sharper lower bound for a trigonometry integral than the one used by
Knopf.