Found:

Braces

PHONOLOGY: a notational convention to abbreviate two rules. EXAMPLE: braces are a means to abbreviate the rules (i) and (ii) as the one rule (iii).

(i)	A -> B	/    C   _____

(ii)	A -> B	/    D   _____

		     C 	
(iii)	A -> B	/  {   } ______
		     D