      ::= PRECEDENCE LEFT terminal_list SEMI
	               | PRECEDENCE RIGHT terminal_list SEMI
	               | PRECEDENCE NONASSOC terminal_list SEMI
terminal_list      ::= terminal_list COMMA terminal_id | terminal_id 
start_spec         ::= START WITH nt_id SEMI | empty
production_list    ::= production_list production | production
production         ::= nt_id COLON_COLON_EQUALS rhs_list SEMI
rhs_list           ::= rhs_list BAR rhs | rhs
rhs                ::= prod_part_list PERCENT_PREC term_id |
 