Supporting Torah learners-Yissachar and Zevulun deal:
Although every single Jew is obligated to study Torah, one who is unable to study Torah, either due to lack of knowledge, or due to lack of time, is to support other people who study. One who supports a Torah learner is considered as if he himself is learning Torah. [Nonetheless, even a Torah supporter must set times for Torah learning in accordance to his capabilities.]
Making a contract with the Torah learner and receiving reward: One is allowed to stipulate with his friend that he [the friend] will learn Torah in exchange for monetary support, and in exchange he will receive part of the reward of his friends learning. This means that they will both split the reward of his Torah learning and the profits that he makes in business. [This implies that the total amount of reward received by the Torah learner is split between the learner and the supporter. Some however learn that the reward of the Torah learner is not diminished at all, and the supporter simply receives an additional reward as if he were to be learning. The above relationship between the Torah learner and supporter is generically referred to as a Yissachar and Zevulun relationship, as Zevulun supported the Torah learning of Yissachar.]
How much monetary support must the Zevulun give the Yissachar in order to receive reward? It is not necessary for the Zevulun supporter to actually give half of all his earnings to Yissachar in order to validate the contract and split the reward from Hashem. He does however have to fully support all the needs of Yissachar in order to split the reward with him. Nonetheless, even partial monetary support merits the receiving of a portion of the reward, commensurate to his level of provision.
Must the Yissachar/Zevulun stipulation be signed into contract?
No. So long as Yissachar is supported by the Zevulun, he receives his portion of reward even if an explicit stipulation was not made, and a contract was not signed. Nonetheless, some are accustomed to make a contract with the Yissachar in order to solidify the agreement in writing, and protect the rights and responsibilities of both sides.
What occurs if the Torah learner does not learn Torah Leshma, or waists his time rather than learn?
In such a case, the Torah learner will be held accountable for his actions. Nonetheless, Hashem will still give the Zevulun supporter the reward, as if he had spent his time learning Leshma, as a good though is translated into action by Hashem.
May the one deduct his Yisssachar/Zevulun contributions from Maaser?
Some Poskim rule that one who helps support a Torah learner through a Yissachar/Zevulun agreement, may not deduct the payments from Maaser. Other Poskim, however, rule that one may deduct it from Maaser. Practically, if the “Yissachar” who is receiving the contributions in exchange for his learning is defined as a pauper according to Jewish law, then one may deduct the funds from Maaser. If, however, the receiver has enough money to live independent of the contributions, then it is not to be deducted from Maaser. Nevertheless, those who deduct the money from Maaser even in this situation, have upon whom to rely, especially if they cannot afford to contribute otherwise.
Rewards and merits given to Torah supporter:
 Yoreh Deah 246:1; See Igros Moshe Y.D. 4:37 in great length pp. 234-250 for various details of this agreement
Other opinions-Opinion of Rambam: The Rambam [Talmud Torah 3:10] rules that it is forbidden for Rabbanim and Torah scholars to support themselves from public funds or to use their Torah knowledge as a source of income. Most Poskim however argue on his ruling. [See Kesef Mishneh ibid; Mishnas Rebbe Tzadok of Yaavetz; Piskeiy Teshuvos 156:1] Practically, the Alter Rebbe [Talmud Torah 4:15] rules that only initially is it forbidden for one to begin his Torah learning with intent to make a livelihood out of it. If however one began his learning Lesheim Shamayim and then came into a situation where he needs to use his knowledge to support himself, then he may do so. The Rebbe explains that an additional allowance applies towards one who is able to sustain himself through other means, but chooses to learn Torah for the sake of Torah, and consequently support himself from it in order so he is able to study. The above prohibition is only if one learns the Torah for the purpose of a profession from which he can make a livelihood, and is thus using it for his own benefit. [Toras Menachem 1:154; printed in Shulchan Menachem 4:273]
 Michaber 246:1; Tur in name of Sifri
 Rama ibid; Tur
 Shlah Shavuos 91b
 Rama ibid
 Shach 246:2; Rishon Letziyon Y.D. 246 [contradicts self from Or Hachaim-see Tzitz Eliezer 15:35]; See Piskeiy Teshuvos 156:26
Must they actually split half of Zevulun’s business proceeds? No. It is not necessary for the Zevulun supporter to actually give half of all his earnings to Yissachar in order to validate the above deal, as will be explained next.
 Or Hachaim Hakadosh Ki Sisa 13; Haflaah 43; Chida in Midbar Kdeimos; See Piskeiy Teshuvos 156:26
 This is similar to a candle which can light other candles and not have its own flame diminished at all. [ibid]
 See Meiam Loaez Vayechi; Chaim Sheol 2:38; Minchas Yitzchak 7:7; Koveitz Mibeis Levi 14
 Piskeiy Teshuvos 156:26; See Shemiras Halashon 5 and 6 regarding the reward given to Torah supporters, without any mention made of a contract and the like.
 See letters of Chazon Ish 47 for an example of a contract in this matter; See also Piskeiy Teshuvos ibid footnote 234
 Beis Shlomo 2:94; Piskeiy Teshuvos ibid
 Rav SZ”A in Minchas Shlomo 2:97-11; Hilchos Maaser Kesafim 14:40; See Igros Moshe Y.D. 4:37-10
 The reason: A such money is considered to be fulfilling ones personal Mitzvah of Torah learning and is not part of the Mitzvah of charity, unless the Yissachar who is learning is indeed defined as a pauper according to Halacha. [Igros Moshe ibid] Alternatively, it is invalid being that the contributer receives a service in return and it is hence similar to a business. Accordingly, even if the receiver is a pauper, it may not be deducted from Maaser. [See Halichos Shlomo ibid]
 Chelkas Yaakov Y.D. 137
 The reason: As all charity is permitted in spiritual and secondary benefit, and hence the fact one benefits from the giving of the charity does not invalidate its charitable status. [ibid]
 Igros Moshe Y.D. 4:37-10 “Certainly there is a Mitzvah to support a Torah learner from ones Chomesh contributions, although not from one’s Maaser contributions, which are obligatory. However, if the Torah scholar is a real pauper, then one may deduct the funds from Maaser.”
 So seems Pashut, as it is permitted to use Maaser money for the sake of fulfilling a Mitzvah that one could not fulfill otherwise, and is not obligated in doing so. Thus, since supporting other to learn Torah is not an absolute obligation, but simply a good act, therefore one may deduct it from Maaser if he does not have other funds to use.
 Shemiras Halashon [Chofetz Chaim] 6; See Piskeiy Teshuvos 156 footnote 236 for a fascinating story brought by the Chofetz Chaim in the name of Rav Chaim Velozhin who had a dream which testified to the truth of this statement.
 Shemiras Halashon [Chofetz Chaim] 5
 Parshas Vayechi
 Shemiras Halashon ibid; Or Hachaim Vezos Haberacha; Bnei Yissachar Tishreiy 10:25
 Shemiras Halashon [Chofetz Chaim] 5
 Chasam Sofer Toldos
 Chulin 92a; See Baal Haturim Shemos 22:26
 Rabbeinu Bechayeh Teruma 10