Complex sentence: The principle was at the time at the heart of the debates of the so-called Vienna Circle which Ayer visited as a young guest, and others including the leading light of the circle, Moritz Schlick were already offering their own papers on the issue.
Split into simpler sentences: The principle was at the time at the heart of the debates of the so-called Vienna Circle which Ayer visited as a young guest. Others, including the leading light of the circle, Moritz Schlick, were already offering their own papers on the issue.