Historical clue formulations

• Puzzler — 2011-11-20
• Leak on a ship, e.g. — 2009-04-22
• "No ___!" — 2007-02-18
• Bit of math homework — 1997-08-12
• Stumper — 1997-01-22
• Bugbear — 1995-12-19
• Gordian knot, for one — 1994-05-04