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- The almost-alphabetic acrostic Al Chet 2 answers
The viduy of the על חטא lists sins from alef to taf, yet the letter samech ס is switched to a sin ש. Why?
(Interestingly I noticed that in between sections of viduy we say סלח לנו מחל לנו כפר לנו, which is roshei teivos סמך. So the samech is there, but hidden.)