Fix empty-set symbol in comments The symbol in the original code is U+00D8 "LATIN CAPITAL LETTER O WITH STROKE" (https://en.wikipedia.org/wiki/%C3%98) which is an uppercase letter in Danish, Norwegian, Faroese, and Southern Sámi alphabets. The symbol that was intended is U+2205 "EMPTY SET" (https://en.wikipedia.org/wiki/Empty_set#Notation). | Before | After | |---|---| |  |  |