Reference for Keritot 24:23

אמר רב ששת

Some refer the discussion to the latter part of the passage: IF OF TWO KINDS, HE IS EXEMPTED; is this not obvious? - Said Resh Lakish in the name of Bar Tutini: We suppose they were eaten in two different dishes and this law is in accordance with R'Joshua who holds different dishes do not combine with one another.

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