Historical clue formulations

• Diamond shape — 2016-04-11
• Diamond, e.g. — 2015-12-18
• Diamond, e.g. — 2015-02-21
• Equilateral figure — 2012-08-22
• Oblique-angled, four-sided figure — 2010-06-14
• Four-sided figure — 2009-08-30
• Skewed square — 1999-08-02
• Squished square — 1994-01-16