ExistentialSubquery = (E,X,I,S,T,S), [SP], '{', [SP], (RegularQuery | (Pattern, [[SP], Where])), [SP], '}' ;
RegularQuery = SingleQuery, { [SP], Union } ;
SingleQuery = SinglePartQuery
| MultiPartQuery
;
Union = ((U,N,I,O,N), SP, (A,L,L), [SP], SingleQuery)
| ((U,N,I,O,N), [SP], SingleQuery)
;
Where = (W,H,E,R,E), SP, Expression ;