In resolving a contradiction between two braitot, the Gemara answers that there is a tannaitic debate (between Rebbi and Rabban Shimon ben Gamliel) regarding the same issue that Rabbi Yochanan and Reish Lakish were debating - when one acquires the produce do they acquire rights to the property itself, meaning do they have rights to sell it? The case where they disagree is one who promised one's possession to one person and after that person's death, they will go to another person and after them to a third person. If the first person sold the property, would the second person be able to demand the property after the death of the first person? Rebbi holds a sale of the property would be invalid. Rabban Shimon ben Gamliel holds that the sale would be valid even though in the case discussed, he thinks one should not be able to sell it ab initio. Rabbi Yochanan held like Rabban Shimon ben Gamliel with one exception. He also added a few cases that would be included within this ruling.  

If one received an etrog as a gift that was to be passed on after their death to another or taken from the estate's funds before they were divided, is one able to fulfill the mitzva or not? While in the former case, they can fulfill the mitzva, Rebbi and Rabban Shimon ben Gamliel would disagree about whether they could sell the etrog.

Is a gift given upon the condition that it be returned considered a gift? Can one fulfill a mitzva with an etrog that they received in this manner?