Pesachim 120A

בראשונה לא. לא מיבעיא קאמר. לא מיבעיא בראשונה ⁠— דקאכיל לתיאבון, אבל באחרונה דילמא אתי למיכל אכילה גסה ⁠— אימא לא, קא משמע לן.

However, if one eats matza before these other foods, no, one may not start eating other foods after matza. The Mishnah apparently supports Rav Yehuda’s opinion. The Talmud rejects this proof: The Tosefta is stated in the style of: Needless to say. Needless to say, one fulfills his obligation if he eats matza before other foods, as he eats it with an appetite. However, if one eats matza after eating other foods, perhaps he will come to eat it in the manner of excessive eating, as he is compelled to eat when he is not hungry. Consequently, you might say that one does not fulfill his obligation if he eats matza after all those other foods. Therefore, the Tosefta teaches us that one may eat matza even after consuming those foods.

מר זוטרא מתני הכי: אמר רב יוסף אמר רב יהודה אמר שמואל: מפטירין אחר המצה אפיקומן. נימא מסייע ליה, אין מפטירין אחר הפסח אפיקומן: אחר הפסח דלא, אבל אחר מצה ⁠— מפטירין.

This is how Mar Zutra taught this discussion: Rav Yosef said that Rav Yehuda said that Shmuel said: One may conclude after the matza with an afikoman. The Talmud suggests: Let us say that the Mishnah supports his opinion: One does not conclude after the Paschal lamb with an afikoman. The Talmud infers: It is after the Paschal lamb that one may not conclude with an afikoman; however, after matza one may conclude with an afikoman.

לא מיבעיא קאמר. לא מיבעיא אחר מצה ⁠— דלא נפיש טעמיה, אבל לאחר פסח ⁠— אימא לא, קא משמע לן.

The Talmud rejects this contention: The Mishnah is stated in the style of: Needless to say. Needless to say, one may not conclude with an afikoman after eating matza, as the taste of matza is slight; however, after the Paschal lamb, one might say that this prohibition does not apply. Therefore, the Mishnah teaches us that it is prohibited to conclude with an afikoman after the Paschal lamb as well.