Judgment :- 1. These second appeals arrise out of two suits disposed of together by both the lower courts. The appellants are the defendants in one of them, which was for declaration of title and partition. The contesting respondent, Thankamma Pillai, was the plaintiff in the other, which was for redemption. Both the lower courts dismissed the suit of the appellants and decreed the suit of the contesting respondent. 2. Two sisters belonging to the Thala Nair community, Mamaperumal and Mamalakshmi, had properties; and Thankamma Pillai, the lineal descendant in the female line of Mamaperumal, and two others, who were themselves lineal descendants in the female line of Mamalakshmi, partitioned the properties under Ex. D-1 in 1115 (February 1940). Thankamma Pillai had two twin brothers Padmanabhan Nair and Velayudhan Nair, who were also parties to one of these suits. It was believed at the time of the partition that properties belonging to women among Thala Nairs were inherited only by their daughters and lineal descendants in the female line and not by male descendants. Ex. D-1 proceeded under that belief. More than nine years after, on 20th December 1949, Thankamma Pillai executed Ex. D-4, which is captioned a settlement deed, but contains provisions of a gift deed. The document recites that out of love and affection for her twin brothers Thankamma Pillai gifted nine items of properties for the donees' maintenance. One of the items in Ex. D-4 was an item taken by Thankamma Pillai under Ex. D-1 and the other eight items were her separate or self acquisitions. About ten years after, in 1959. one of the brothers, Padmanabhan Nair, conveyed his share in the suit item, another item in Ex. D-1, under Ex. P-1 to one of the appellants; and both the appellants now claim title to such share conveyed by Padmanabhan Nair. 3. The lower courts, more so the lower appellate court, thought that unless Padmanabhan Nair was prepared to surrender the benefit he obtained under Ex. D-4, he or his assignees could not claim his share in the tarwad properties, which came to Thankamma Pillai under Ex. D-1. It is this decision that is being challenged in these second appeals. 4. Regarding the facts there cannot be much dispute. The parties were under the impression when Ex. D-1 was executed that descendants in the female line alone were entitled to properties of women among Thala Nairs. D-1. It is this decision that is being challenged in these second appeals. 4. Regarding the facts there cannot be much dispute. The parties were under the impression when Ex. D-1 was executed that descendants in the female line alone were entitled to properties of women among Thala Nairs. Therefore, the twin brothers of Thankamma Pillai were not made parties to Ex. D-1, though they were then in existence, of course, as minors. Thankamma Pillai as dw.1 has said that she executed Ex. D-4 and gifted some items to her brothers, because they had no right to any property under Ex. D-1. The recital in Ex. D-4 also points in this direction. It was only in the decision of this court in Sankaran Nadar v. Govindan Nair (1960 KLT. 579) that the position was made clear that the Travancore Nair Act applied to Thala Nairs as well; and that that community was not governed by any special custom on this question. The question then is whether Padmanabhan Nair or his assignees can claim Padmanabhan Nair's share in the one item of property, which Thankamma Pillai took under Ex. D-1 and which is the subject-matter of the suit. 5. The counsel of the contesting respondent tries to bring these cases within any one or more of the following doctrine: (1) estoppel: that a person cannot say at one time that a transaction is valid and thereby obtain some advantage to which he could only be entitled on the footing that it is valid, and at another time say that it is invalid for the purpose of defeating another who is entitled to obtain an equal advantage with him on the footing that it is valid; (2) election: that a person taking the benefit of an instrument must also bear its burden and that he cannot take under and against the same instrument; and (3) approbation and reprobation: that a person may not approbate and reprobate, f. e., that he, having a choice between two courses of conduct, is to be treated as having made an election from which he cannot 'resile; but he will not be regarded as having so elected unless he has taken a benefit under or arising out of the course of conduct which he has first pursued and with which his subsequent conduct is inconsistent. All these doctrines presuppose a conscious and deliberate exercise of right. All these doctrines presuppose a conscious and deliberate exercise of right. But, in the present cases the parties acted under a mutual mistake regarding the law of inheritance applicable to them. Still, I do not think that the position will be different. If under a mutual mistake one party suffered a detriment and the other derived a benefit, which would not have happened but for the mistake, the latter cannot subsequently claim to dispel the mistake and claim a benefit thereby, unless he is prepared to surrender the benefit he already obtained under the mistake. This, I think, is an obvious principle of equity, which no court will hesitate to enforce. 6. In these cases, the suit item was one of the items included in Ex. D-1, in which Padmanabhan Nair also had a share. But, under a mutual mistake that Padmanabhan Nair and his brother had no right to the properties in Ex. D-1, Thankamma Pillai conveyed another item Ex. D-1 and eight other items belonging to her as her self acquisition to her brothers, which she would not have done, if the brothers also had a right to the properties covered by Ex. D-1. Having taken the eight other items belonging exclusively to Thankamma Pillai under Ex. D-4, Padmanabhan Nair and his assignee cannot claim Padmanabhan Nair's share in the suit item saying that he is entitled to it under the law of inheritance applicable to Thala Nairs. If they want to claim that, Padmanabhan Nair must, in equity, surrender his share in the eight items admittedly belonging to Thankamma Pillai, which Padmanabhan Nair and his brother obtained under Ex. D-4. 7. The decisions of the lower courts are thus right; and they are confirmed. The second appeals are dismissed: and the contesting respondent, Thankamma Pillai, will get half costs in each of the cases. Dismissed.