User blog comment:Bubby3/My version of NDAN/@comment-11227630-20180212011908

From your first 3 lines I can infer that @ reduces to From your 7th line I can infer that @, reduces to So @ and {1@,2} reduce to different things.
 * ` when b=1 (b is the iterator), or
 * {1...{1{1,,...,,3}2}...2} with b-ple comma and b-2 2's when b>1.
 * ,, when b=1, or
 * {1...{1{1,,...,,3}2}...2} with (b+1)-ple comma and b-2 2's when b>1.

From your 4th line I can infer that {2@,2} reduces to @1@1...@1@ with b @'s, which doesn't follow "the case of dimension".