Historical clue formulations

• Trigonometry symbols for angles — 2020-03-25
• Sorority members such as Ann-Margret and Laura Bush — 2011-02-15
• Trig symbols — 2010-11-19
• Certain sorority members — 2008-05-21
• Angle symbols, in geometry — 2007-02-03
• Some sorority women — 2006-02-15
• Some sorority women — 2002-07-31