Historical clue formulations

• Conclusive proof provider — 2020-10-16
• Chemistry exam? — 2019-01-19
• Decisive assessment — 2018-03-25
• Conclusive trial — 2012-05-20
• Proof provider — 2007-04-14
• Critical step in analysis — 2005-08-26
• Conclusive trial — 2004-06-30
• Critical step — 2000-05-13
• Defining challenge — 1995-06-23