Responsa for Nedarim 112:10

הא כיצד עומד בצד המשקוף ויסגיר ומנין שאם הלך לביתו והסגיר או שעמד תחת השקוף והסגיר שהסגירו מוסגר ת"ל (ויקרא יד, לח) והסגיר את הבית מכל מקום שאני גבי בית דכתיב מן הבית עד שיצא מן הבית כולו:

<b><i>GEMARA</i></b>. Whence do we know that the outskirts of a town are as the town itself? — R. Johanan said, Because it is written, and it came to pass, when Joshua was in Jericho etc.<span class="x" onmousemove="('comment',' Josh. V, 13. ');">¹⁷</span> Now, what is meant by 'in Jericho'? Shall we say, actually in Jericho: but is it not written. Now Jericho was straitly shut up because of the children of Israel?<span class="x" onmousemove="('comment',' Ibid. VI, 1. ');">¹⁸</span> Hence it must mean in its outskirts.<span class="x" onmousemove="('comment',' Which are referred to as the town itself. ');">¹⁹</span> Then say that it means even in the tehum?<span class="x" onmousemove="('comment',' Perhaps Joshua was stationed within the tehum of Jericho which is spoken of as 'in Jericho'. ');">²⁰</span> — But with respect to the tehum it is written, And ye shall measure without the city [in the east side two thousand cubits etc.].<span class="x" onmousemove="('comment',' Num. XXXV. 5. ');">²¹</span> BUT ONE WHO VOWS [ABSTINENCE] FROM A HOUSE IS FORBIDDEN FROM THE DOOR-STOP AND WITHIN. But not from the door-stop and without.<span class="x" onmousemove="('comment',' I.e., the steps or threshold up to the doorstep are permitted. ');">²²</span> R. Mari objected: Then the priest shall go out of the house;<span class="x" onmousemove="('comment',' Lev. XIV, 38. The priest, after inspecting the leprous house for the first time, was to go out and have it sealed up for a week. ');">²³</span> I might think that he goes home and then has it probably of the width. To these a cross-piece was attached, the whole forming a frame over which a net or curtain was slung. shut up; therefore it is taught, to the door of the house.<span class="x" onmousemove="('comment',' Lev. XIV, 38. ');">²⁴</span> If [I had only to go by] 'to the door of the house,' I might think that he stands under the lintel and closes it; therefore, it is written, ['Then the priest shall go] out of the house', implying that he must go right out of it — How so? He must stand at the side of the lintel and close it. Yet how do we know that if he goes home and has it closed, or stands under the lintel and shuts it, that it is validly shut? From the verse, And shut up the house,<span class="x" onmousemove="('comment',' Ibid. ');">²⁵</span> implying no matter how it be done.<span class="x" onmousemove="('comment',' Now, when one is outside the lintel, he is also, of course, outside the door-stop: yet he is not regarded here as being right out of the house, thus contradicting the implication of the Mishnah that without the door-stop is not part of the house. ');">²⁶</span> — In the case of the [leprous] house it is different, because it is written 'out of the house', implying that he must go right out of the house.

Teshuvot Maharam