Yevamot

A proselyte may, according to Pentateuchal law, sit in judgment  on a fellow proselyte, for it is said in the Scriptures, Thou shalt in any wise set him king over thee, whom the Lord thy God shall choose; one from among thy brethren shalt thou set king over thee;  only when set over thee  is he required to be one from among thy brethren;  when, however, he is to judge his fellow proselyte he may himself be a proselyte.  If his  mother was an Israelitish woman he may sit in judgment even on an Israelite.  In respect of halizah, however, [no man is eligible as judge] unless both his father and his mother were Israelites for it is said, And his name shall be called in Israel. Rabbah stated in the name of R. Kahana in the name of Rab: If Elijah should come and declare that halizah may be performed with a foot-covering shoe,  he would be obeyed; [were he, however, to declare that] halizah may not be performed with a sandal,  he would not be obeyed, for the people have long ago adopted the practice [of performing it] with a sandal. R. Joseph, however, reported in the name of R. Kahana in the name of Rab: If Elijah should come and declare that halizah may not be performed with a foot-covering shoe,  he would be obeyed; [were he, however, to declare that] halizah may not be performed with a sandal,  he would not be obeyed, for the people have long ago adopted the practice [of performing it] with a sandal. What is the practical difference between them?  — The practical difference between them is [the propriety of using] a foot-covering shoe ab initio. According to him, however, who stated [that it was proper to use  it] even ab initio, surely, [it may be objected] we learned: IF A WOMAN PERFORMED THE HALIZAH WITH A FOOT-COVERING SHOE, HER HALIZAH IS VALID [which  implies validity only] after the action had been performed but not ab initio. — The same law  is applicable even [where the shoe was used] ab initio. As, however, it was desired to state in the final clause: BUT IF WITH A SOCK IT IS INVALID, [a law] which applies even after the action had been performed, a similar expression  was also used in the first clause. [On the question of] using a foot-covering shoe  ab initio Tannaim differ. For it was taught: R. Jose  related, 'I once went to Nesibis where I met an old man whom I asked, "Are you perchance acquainted with R. Judah b. Bathyra?" and he replied, "Yes; and he in fact always sits at my table". "Have you ever seen him arranging a halizah ceremony for a sister-in-law?" [I asked]. "I saw him arranging halizah ceremonies many a time", he replied. "With a foot-covering shoe [I asked] or with a sandal?" — "May halizah be performed", he asked me' "with a foot-covering shoe?" I  replied: Were that [not] so, what could have caused  R. Meir to state that halizah if performed with a foot-covering shoe is valid, while R. Jacob reported in his  name that it was quite proper to perform [even] halizah ab initio with a foot-covering shoe!' With reference to him who ruled that it was not proper ab initio [to perform halizah with a foot-covering shoe] what could be the reason? If it be suggested: Because [the loosing of] the upper  [may be described as] from off  and [the loosing of the] thong  as 'from off of the from off', [a performance which is not in accordance with] the Torah which said, from off  but not 'from off of the from off'; [it could well be retorted that] if such were the reason [the halizah should be invalid] even when actually performed. — This  is a preventive measure against the possible use of a flabby  shoe or even half a shoe. Said Rab: Had I not seen my uncle  arranging a halizah with a sandal that had laces I would have allowed a halizah only with an Arabian sandal which can be more firmly fastened. And in respect of our [kind of sandal] though it has a knot,  a strap also should be tied to it,  so that the halizah may be properly performed. (Mnemonic: You permitted a sister-in-law a sandal.)  Rab Judah reported in the name of Rab: The permissibility of a sister-in-law to marry a stranger takes effect as soon as the greater part of the heel  is released. An objection was raised: If the straps of a foot-covering shoe or of a sandal were untied  or if [the levir] slipped [it off from] the greater part of his foot,  the halizah is invalid.  The reason then  is because it was he that slipped it off; had she, however, slipped it off, her halizah would have been valid; [and, furthermore this applies to] the greater part of the foot only  but not to the greater part of the heel!  — The 'greater part of the foot' has the same meaning as 'the greater part of the heel'; [and the reason] why he calls it 'the greater part of the foot' [is] because all the weight of the foot rests on it. This  provides support for R. Jannai. For R. Jannai stated: Whether [the levir] untied [the straps] and she slipped off [the sandal] or whether she untied the straps and he slipped off the sandal, her halizah remains invalid, unless she unties the straps and she slips off the sandal. R. Jannai enquired: What is the law if she tore it?  What if she burnt it?  Is the exposure of the foot necessary,  and this has here been effected,  or is 'taking off' necessary, which has not taken place here?  — This remains undecided. R. Nehemiah enquired of Rabbah: What is the law in the case of two shoes one above the other? — How is this enquiry to be understood? If it be suggested: That she  drew off the upper one and the lower one remained, surely, the All Merciful said: From off  but not 'from off of the from off'! — Such enquiry is necessary only where she tore the upper one and removed the lower one while the upper one remained [on the levir's foot], the question being whether  the requirement is the 'taking off' which has been done,  or whether the exposure of the foot is necessary which was not effected here?