Historical clue formulations

• Like some verbs: Abbr. — 2016-10-03
• Like some verbs: Abbr. — 2012-10-27
• Like some verbs: Abbr. — 2009-08-30
• Preface: Abbr. — 2008-10-18
• Like some verbs: Abbr. — 2007-09-16
• Verb type: Abbr. — 2006-10-09
• Like 101 courses: Abbr. — 2006-05-05
• Like some verbs: Abbr. — 2003-10-26
• Like some verbs: Abbr. — 2002-12-25
• Foreword: Abbr. — 2002-11-19
• Verb type: Abbr. — 2002-07-02
• Foreword: Abbr. — 2001-07-04
• Verb type: Abbr. — 1995-01-29