Generalized unions and intersections
In view of the associative laws, the expressions
S1 ?S2 ?... ?Sn, also denoted by ?Si,
S1 ? S2 ?... ? Sn, also denoted by ?Si,
are unambiguous (no need in parentheses):
x?(S1?S2?... ?Sn) iff x?S1 ? x?S2 ? … ? x?Sn
x?(S1 ? S2 ?... ? Sn) iff x?S1 ? x?S2 ? … ? x?Sn