@property_cached<EOL><INDENT>def ids(self):<DEDENT>
as_list = [seq.description.split()[<NUM_LIT:0>] for seq in self]<EOL>as_set = frozenset(as_list)<EOL>assert len(as_set) == len(as_list)<EOL>return as_set<EOL>
A frozen set of all unique IDs in the file.