Historical clue formulations

• Atmospheric prefix — 2021-01-10
• Gas: Prefix — 2017-04-08
• Prefix with -form — 2015-02-15
• Gas: Prefix — 2010-05-28
• Gas: Prefix — 2004-06-06
• Gas: Prefix — 1998-06-20
• Ethereal: Prefix — 1998-02-05