Reference for Eruvin 56:7

רבי יהודה אומר קור הרי הוא כעץ לכל דבריו אלא שניקח בכסף מעשר וכפניות הרי הן כפרי לכל דבריהם אלא שפטורות מן המעשר

Unripe dates, however, may be purchased with [second] tithe money and they are also susceptible to food defilement. R'Judah ruled: The white heart of a palm is treated as wood in all respects, except that it may be purchased with [second] tithe money,<span class="x" onmousemove="('comment',' The difference between this ruling of R. Judah and that of the first Tanna is discussed infra.');">¹⁰</span> while unripe dates are treated as fruit in all respects except that th are exempt from the [second] tithe?<span class="x" onmousemove="('comment',' Since they are still in an unripe state. Tosef. M. Sh. I. Now since the Baraitha speaks of 'food defilement' in connection with the unripe dates it is obvious that they are regarded as a food; why then were they not allowed to be used in the preparation of an 'erub?');">¹¹</span>

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