ONE IS YOTZEI BIRKAS HA'TORAH THROUGH AHAVAH RABAH [Birkas ha'Torah: Ahavah Rabah]
(Rav Yehudah): If one already said Keri'as Shema (and its Berachos), he does not bless Birkas ha'Torah, for Ahavah Rabah exempts him.
(Mishnah): They (Kohanim of the Mishmar) said one Berachah, Aseres ha'Dibros, Shema...
(Rav Yehudah): They blessed Ahavah Rabah.
(R. Zerika): They blessed Yotzer Or.
Rosh (1:13): The Yerushalmi says that one was Yotzei Birkas ha'Torah through Ahavah Rabah only if he learned immediately afterwards in that place. Then, it looks like it is for Birkas ha'Torah, just like it is for Keri'as Shema. He need not bless again the entire day, even if he ceased learning and resumes learning again later.
Rashi (11b DH she'Kevar): Ahavah Rabah has the essence of Birkas ha'Torah - "v'Sen b'Livenu Lilmod u'Lelamed Lishmor v'La'asos u'Lekayem Es Kol Divrei Salmud Torasecha u'Selamdem Chukei Retzonecha."
Tosfos (11b DH she'Kevar): The Yerushalmi says that one was Yotzei through Ahavah Rabah only if he learned right after in that place. People asked R. Yitzchak 'why don't we repeat Birkas ha'Torah when we learn? We are occupied with other matters, and we do not learn after Shacharis until midday or later!' He answered that we do not follow the Yerushalmi. Since the Bavli did not mention this, one need not learn immediately. Also, even the Yerushalmi said so only about Ahavah Rabah, which is primarily for Keri'as Shema, and not for Birkas ha'Torah. Therefore, it exempts Birkas ha'Torah only if he learned immediately without Hesech ha'Da'as (diverting his mind).
R. Yonah (5b DH u'Lefi): The Ri explained the Yerushalmi as follows. Ahavah Rabah is obligatory only for Keri'as Shema. If one learns right after saying Shema and praying, this shows that read Shema with intent for Mitzvas Keri'as Shema, and also for the obligation to learn. (Therefore, he is Yotzei Birkas ha'Torah.) If he learns only afterwards, this shows that read Shema with intent only for Mitzvas Keri'as Shema, so he was not Yotzei Birkas ha'Torah.
Rashba (11b DH Hishkim): The Ra'avad says that some texts of the Yerushalmi say that one was Yotzei through Ahavah Rabah 'only if Kara (he read) immediately'. If so, as long as he read Keri'as Shema after Ahavah Rabah, he is exempted (from Birkas ha'Torah) the entire day. Some texts say 'only if Shanah (he learned) immediately'. If so, Ahavah Rabah exempts only from what he learns right after, but if he interrupted and returned to learn, he must bless again. Tosfos says that if one normally learns, and interrupts when he must work with intent to resume learning when he can, he need not bless again even according to the Yerushalmi. They brought a proof from R. Tam. He obligates a new Berachah Leshev ba'Sukah only for a new meal, even if one left the Sukah for his affairs and later decided to sleep. All the more so we need not bless again, for we do not divert our minds from learning. Therefore, our custom is not to bless (again).
Shulchan Aruch (OC 47:7): Birkas Ahavas Olam exempts from Birkas ha'Torah, if one learned immediately without interruption.
Beis Yosef (DH v'Im): R. Yonah and the Mordechai (27) say like Tosfos, that one was Yotzei through Ahavah Rabah only if he learned immediately afterwards.
Beis Yosef (DH v'Im): Why does the Yerushalmi say that one was Yotzei only if he learned immediately afterwards? He always learns right after Ahavah Rabah, i.e. he says Keri'as Shema! Perhaps the Yerushalmi holds like the opinion that in the Mikdash they blessed Yotzer Or before Keri'as Shema... and afterwards they blessed Ahavah Rabah. It teaches that in such cases, it exempts Birkas ha'Torah only if one learned right after. Also, we can say that Keri'as Shema and Tefilah are not considered learning regarding Birkas ha'Torah. Supplications are not learning. For this, Keri'as Shema is like Tefilah.
Beis Yosef (DH v'Heicha, citing Mahari Avuhav): If one blessed Ahavah Rabah before Birkas ha'Torah, the Rashba was unsure whether one may bless Birkas ha'Torah afterwards, for the Tosafists hold that Ahavah Rabah does not exempt the entire day.
Mishnah Berurah (13): The Shulchan Aruch discusses Ahavas Olam, like he rules below (59:1). The Rema holds that we say Ahavah Rabah at Shacharis. Clearly, Ahavas Olam similarly exempts at Ma'ariv for the same reason. This is relevant to one who transgressed and slept a fixed sleep on a bed beforehand. The Mechaber (Sa'if 11) holds that this is a Hefsek for Birkas ha'Torah. Even though our custom is like the lenient opinion there, it is good to intend in Ahavas Olam to be Yotzei according to most Poskim who are stringent.
Note: Sa'if 11 discusses one who slept during the day. The Mishnah Berurah agrees that we bless after sleeping at night! Why did he say 'one who transgressed and slept...'? It was Midas Chasidus of David ha'Melech not to sleep during the day (OC 4:16). One should judge whether sleep during the day will help his Avodas Hash-m (Mishnah Berurah 4:36)! Perhaps he means that he 'transgressed' the warning of Avos 3:10 'sleeping in the afternoon removes a person from the world'.
Bi'ur Halachah (DH Birkas): If one does not normally learn, the Magen Avraham (9) explains that the Mechaber (Sa'if 10) obligates him to bless before learning. However, if he learns right after Ma'ariv, Ahavas Olam exempts him, even if he did not intend at the time to exempt learning.
Bi'ur Halachah (DH Poteres): R. Yonah connotes that if one knows that he did not intend (that Ahavah Rabah be Birkas ha'Torah), or he remembered only after Ahavah Rabah that he did not say Birkas ha'Torah, he was not Yotzei through Ahavah Rabah. The way the Rosh explains the Yerushalmi, we do not distinguish like this. The Mishbetzos Zahav (52:1) says that one can intend not to exempt Birkas ha'Torah, and then all agree that he was not Yotzei, even if Mitzvos do not need Kavanah. Why didn't he mention R. Yonah's opinion?
Mishnah Berurah (15, citing the Levush): Even if he prayed and finished the Tefilah, this is not called a Hefsek, since he learned immediately afterwards.
Bi'ur Halachah (DH Im): Or Zaru'a ha'Gadol says a bigger Chidush. He is concerned only for a long Hefsek between Ahavah Rabah and learning, but all matters of Tefilah, and also going to get Seforim to bring them to the Beis Midrash, are not a Hefsek. It seems that this is only if he did not interrupt with words not connected to learning.
Kaf ha'Chayim (14): The Rashba says that according to the text "Shanah immediately", the Ra'avad holds that even if he learned immediately, it exempts only that learning, but not (if he stops, and resumes learning) later in the day. The Pri Chodosh holds like this, and the Levush connotes like this. According to the Poskim that Birkas ha'Torah is mid'Rabanan, we are lenient, so if he learned right after, we rely on those who say that this exempts the entire day.
Kaf ha'Chayim (15): Here we say that Ahavas Olam exempts Birkas ha'Torah. In Siman 139:9, we say that one who was Oleh l'Torah before saying Birkas ha'Torah (he blesses Asher Nasan Lanu and Asher Bachar Banu) is exempted from Birkas Asher Bachar Banu. This implies that Ahavas Olam exempts from all three Berachos of Birkas ha'Torah, but the Oleh still needs to bless Asher Kidshanu b'Mitzvosav... and Ha'arev Na... The Maharshal and many others say so.
Shulchan Aruch (8): It is not clear whether it suffices to read Keri'as Shema right after without a Hefsek Therefore, one must be careful to say Birkas ha'Torah before Ahavas Olam.
Gra: There are two ways to explain the Yerushalmi. 1) Ahavah Rabah exempts only what he learns right after. Even if he learned right after, it does not exempt what he will learn later (after he ceased learning). If so, the same applies to Birkas ha'Torah. 2) Ahavah Rabah exempts the entire day only if he learned immediately. Perush (2) is difficult, for why wasn't it enough that he said Keri'as Shema immediately? Perush (1) is difficult, for why wasn't this taught about Birkas ha'Torah itself? Due to this, the Rosh favored Perush (2). It looks like Birkas ha'Torah only if he learned right after. The Rosh says that even according to Perush (1), he must learn right after Birkas ha'Torah. It is just like Ahavah Rabah. The Gemara could have taught about either one. For any Berachah on a food or Mitzvah, a Hefsek before starting (to eat, or the Mitzvah) disqualifies the Berachah, but a Hefsek in the middle does not. The Tur holds that the Rosh concluded like this, for he says so in Teshuvah 4:2. Tosfos connotes that after Birkas ha'Torah, one need not learn immediately. The Maharshal and Bahag say that really, Tosfos holds like the Rosh. The Rambam and other Poskim hold like this. Really, there is no Safek here. Perush (1) is more reasonable. Perush (2) was written just for a mere stringency (since one could explain differently).
Mishnah Berurah (17): Also Eliyahu Rabah brought many Poskim who say that Keri'as Shema does not help. If one read Shema after three hours, this is like reading in the Torah. Perhaps all agree that this exempts, even if he did not learn right after.
Mishnah Berurah (18): One must be careful, lest he forget to learn right after.
Bi'ur Halachah (DH v'Yesh): R. Akiva Eiger says that even the Mechaber wrote 'it is not clear' only to make people careful, but he agrees that if one did not learn right after, he must bless.
Kaf ha'Chayim (17): According to the Beis Yosef's first answer, the Yerushalmi teaches about one who did not say Keri'as Shema right after Ahavas Olam. If he said it right after, it exempts Birkas ha'Torah. His second answer holds that Keri'as Shema does not exempt. This is why he wrote 'it is not clear.' Others say that surely Keri'as Shema is not enough. However, we hold like the Poskim that Birkas ha'Torah is mid'Rabanan, so we are lenient about a Safek, and Keri'as Shema suffices even if he did not learn right afterwards. However, one should be careful to bless Birkas ha'Torah beforehand and not rely on this. Kitzur Shulchan Aruch says so.
Mishnah Berurah (1): If one remembered after Shacharis that he did not bless Birkas ha'Torah, he should not bless now, for he blessed Ahavah Rabah. Perhaps this is even if he did not learn right after praying. Since many say that Birkas ha'Torah is mid'Rabanan, he should ask someone else to exempt him later, or intend that Ahavah Rabah be Birkas ha'Torah and learn right after praying.