How the Adage ‘Sheker (Falsehood) Has No Feet’ Bears on Halacha
The Rule of Mukaf Gevil
The components of the kuf
The main body of the kuf is shaped like a chaf whose base is shortened on the left side. The left leg resembles a mini final nun (with a narrow top and short leg). If the main body looks like a reish, there is a machlokes as to whether it is kosher. If the left leg looks like a vav or a straight line (no top), it is kosher. The main body and the leg should be close enough to look like one letter but should not touch.
How the adage ‘sheker has no feet’ bears on halacha
The Gemara states, "Why does sheker have only one foot? Because it will not endure." The Rishonim explain that the three letters shin, kuf and reish, which compose the word sheker, have only one leg each — unlike other letters that have two legs or a flat base. The poskim infer from this that the shin should sit on a [left-handed] point and not a flat base. There is a machlokes as to whether a shin with a flat base is kosher b’dieved. According to one opinion, the single leg of sheker refers only to the leg of the letter kuf (upon which the word sheker stands).
(משנת סופרים אות ש; ביאורים ומוספים דרשו, 3)
The rule of mukaf gevil
There is a rule known as mukaf gevil which mandates that every letter of stam must be completely surrounded by parchment. Chazal derived this halacha from the word u’chesavtom, which can be divided into two words – u’chesav and tom-i.e. "complete writing." This means that every letter must be formed completely and surrounded by parchment to be fully recognizable. Lechatchila, the rule of mukaf gevil applies to the white interior of letters that close on at least three sides (e.g. beis, heh, ches). There are three areas which require particular attention: 1.There must be space between the end of a line and the edge of the klaf. 2. There must be a distinct separation between all letters (two letters may not touch at any point). 3. No letter may abut a hole in the klaf.
(כללי ‘מוקף גויל’)
A fay is formed from an oversized chaf and an upside down inverted vav hanging inside it. L’chatchila, the interior of the fay should resemble a beis.
The Asheknazi alphabet is referred to as ksav Beis Yosef, and the Sefardi alphabet ksav Velish. According to many poskim, each ksav is kosher for the other group only b’dieved. According to some poskim, this is true even l’chatchila. There is an opposing opinion which holds that Ashkenazim may not fulfill their obligation with ksav Velish even b’dieved.
The tzadi is formed from a yud and a nun. In the standard Ashkenazi script a regular yud is used; in the Sefardi and Kabbalistic ksav an inverted yud is used. Both forms of the letter can be found in ancient sources.