Responsa for Bava Batra 323:3

מאי שנא שני שיטין דלמא מזייף וכתב שיטה אחת נמי מזייף וכתב אלא לאו שמע מינה אין למדין משיטה אחרונה שמע מינה

you [derive] this? [The other] replied to him: Because it was taught, If the [signatures of the] witnesses were removed two lines from the text, [the deed] is invalid; [if only] one line, [it is] valid. Why are two lines different [from one line]? Because one might commit forgery and add<span class="x" onmousemove="('comment',' Lit., 'write'. ');">³</span> [some unauthorised matter]! [In the case of] one line also [might not one] commit forgery and add<span class="x" onmousemove="('comment',' Lit., 'write'. ');">³</span> [some spurious matter]? Must we not then conclude [that] the last line cannot be taken as a determining factor'? This proves it.

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