converts a following bu-letteral into a sumti representing the musical double flat note with that name.
The next bu-letteral is absorbed and a double flat accidental is given to it; e.g. "zi'e'u gy" means "the note G-double-flat". To refer to a different multiple of the flat, use "zi'e'o" with a subscript instead. The first two syllables of the cmavo in the zi'e'a series were chosen for the similarity to "zgike". See also: zi'e'a, zi'e'e, zi'e'i and zi'e'o.