I've never seen it in math proper, is what I meant, but ...
The { [ ( ) ] } hierarchy is used in chemical nomenclature. It is specified by IUPAC (International Union of Pure and Applied Chemistry).For example:acetone (/R/)-/O/-{2-[4-(α,α,α-trifluoro-/p/-tolyloxy)phenoxy]propionyl}oxime
... it looks like someone spotted the mythical beast, U+666! Or is it just a mutation ascended from a bath of noxious chemical ooze? Stephan
