Historical clue formulations

• Kind of strength — 2015-12-06
• Kind of strength related to stress — 2015-05-13
• Capable of being stretched — 2014-04-09
• Kind of strength — 2013-01-20
• Kind of strength — 2009-04-10
• Kind of strength — 2003-12-21
• Kind of strength — 1999-02-07