Historical clue formulations

• Like the study of the kabbalah — 2026-01-21
• Like much tax law or ancient philosophy — 2025-04-20
• Requiring rare knowledge — 2022-11-21
• Way out there — 2019-10-27
• Like most philosophy dissertations — 2014-09-13
• Way out there — 2010-01-02
• For initiates only — 2008-11-09
• Rarefied — 2006-05-27
• Indecipherable — 2005-10-30
• Understood by few — 2005-02-09
• Shrouded in mystery — 2002-11-22
• Incomprehensible — 2002-11-17
• Abstruse — 1999-07-13
• Secret — 1998-09-05
• Abstruse — 1998-04-23
• Arcane — 1994-08-04