Uh oh - I take back my Heterim. I just found this:
http://www.theyeshivaworld.com/weekly_torah.php?id=251 Thinking Torah Thoughts In A Bathroom[/size][/color]
One is not allowed to think in learning while he is in a bathroom.(57) Rather one should think about his business dealings etc.(58) On Shabbos since one should not think about business one should think about buildings.(59) If one has learning on his mind all the time then he is considered an o'nes and thinking in learning is permitted.(60) If one is using the bathroom and a thought about a certain lady comes into his mind then he may think in learning.(61) Sometimes the bathroom of a shul is situated in such a way that one hears devarim sh'be'kedusha while in the bathroom. In this situation one is considered an o'nes and thinking in learning is permitted.(62) It would seem that one may think in learning if one passed gas.(63) One is forbidden to think about Hashem in the bathroom.(64) There is a discussion in the poskim whether or not one is permitted to think about learning while he is in the shower (when there is no toilet in the room).(65) Some poskim say it is permitted for one to think in learning in a room that only has a tub.(66)
Footnotes
(57) Refer to Gemorah Shabbos 40b, Rashi "l'harher," Rosh 3:12, Gemorah Shabbos 150a, Rambam Hilchos Krias Shema 3:4, Shulchan Aruch 85:2, Levush 85:2, Elya Rabba 85:2, Pri Megadim Eishel Avraham 2, Machtzis Ha'shekel 85:1, Birchei Yosef 85:3, Ben Ish Chai Vayetzeh 1:16, Shulchan Aruch Harav 1, Aruch Ha'shulchan 2. This applies to the four amos from where any odor has gone away (Mishnah Berurah 7, Kaf Ha'chaim 7). (58) Magen Avraham 85:1, Shulchan Aruch Harav 1, Mishnah Berurah 6, Kaf Ha'chaim 4, Tehilla L'Dovid 5:1, Masef Lechul Hamachanus 3:8. One can think of how low he is and where he came from (Mishnah Berurah ibid). (59) Be'er Heitiv 85:1, Machtzis Ha'shekel 85:1, Shulchan Aruch Harav 1, Tehilla L'Dovid ibid, Masef Lechul Hamachanus ibid. (60) Refer to Yerushalmi Berochos 3:4, Rashi Zevachim 102b l'onsa," Kesef Mishna Hilchos Krias Shema ibid, Bais Yosef 85, Drisha 85:1, Sharei Teshuva 85:1, Pri Megadim M.Z 85:1, Pri Chadash, Mishnah Berurah 8, Kaf Ha'chaim 5, see Shiurei Beracha 85:1, Birchei Yosef 1, Shulchan Hatohar 85:1 who frown upon thinking in learning even in this situation. (61) Magen Avraham 4, Shulchan Aruch Harav 4, Mishnah Berurah 13, Aruch Ha'shulchan 2, Kaf Ha'chaim 16. (62) Tzitz Eliezer 13:1:2, (63) Eishel Avraham Butchatch 79:9. (64) Chuchmas Shlomo 85, Lehoros Nosson 1:1, Tzitz Eliezer 13:1:3. (65) Refer to Divrei Chachumim page 21:10, see Kedushas Hamachanei K'hilchosa pages 242-24 in depth. (66) Yabea Omer O.C. 7:27:4. Refer to Yabea Omer O.C. 5:11.
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It would seem you might be allowed to bring the big book in the bathroom but not read the part about Hashem, if you can find any...
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