delivered the opinion of the Court.

A petition was filed in the Registry of Property of Ponce requesting the registration of six real properties situated in said municipality in favor of appellants Roberto, Gloria, and Iván Gerardo, all surnamed Clavell Rodriguez, as testamentary trustees designated by Cosme Clavell Rodríguez, and of the minors Gloria Milagros and Gustavo Clavell Rosa, as beneficiaries. The following complementary documents were attached: 1 — certified copy of the open will executed by Cosme Clavell Rodriguez, No. 66 of June 2, 1956, before notary Práxedes Alvarez Leandri; 2 — certificate issued by the Clerk of the Supreme Court of Puerto Rico certifying the registration of said will in the Registry of Wills and proof that it did not appear that the same had been revoked or modified in any manner whatsoever subsequent to its execution; 3 — certified copy of deed No. 66 of June 29, 1962, before notary Práxedes Alvarez Leandri by virtue of which a document signed by the appellants before notary R. Davis Vázquez accepting the designation of tutors and trustees was protocolized; 4 — certified copy of the letters testamentary issued in favor of appellants by the Superior Court, Ponce Part, on August 7, 1961; and 5 — the original receipt of inheritance tax issued by the Secretary of the Treasury in relation to the estate of the aforementioned testator.

In the testamentary provisions under consideration, the testator instituted as heirs his children Gloria Milagros and *339Gustavo, in equal parts of his entire estate; he stated that “Although by operation of law, Raquel Rosa, the natural mother of his minor children, has the patria potestas over them, in furtherance of the welfare and education of said children, the testator has deemed it convenient to designate . . . tutors . . . because he believes that the minors’ mother does not have sufficient academic preparation and the intellectual and emotional maturity necessary to assume the administration of the minors’ property and to govern and provide them with a painstaking education and training,” for which reason he designated appellants as his children’s tutors, relieving them from the obligation to give bond; and finally, he constituted a trust over all his estate, designating the appellants herein as trustees, without obligation to give bond, in order that after his death “they take possession of the estate, administer it, collect the income produced in favor of the testator’s minor children . . . He established that the trust would last until the children attained majority, and enlarging their powers, he authorized them to encumber and alienate the properties in trust if it were useful, necessary, and convenient for the beneficiaries and in order to execute the trust.

The registrar issued the following note which contains his view of qualification:

“This document, is hereby recorded in view of the complementary documents in favor of the trustees . . . but limiting the registration to two-thirds thereof equivalent to the extra and free portion subject to the suspensive condition that the minor beneficiaries’ mother accept the inheritance in their behalf (art. 16 of the Mortgage Law), and the record is hereby denied as to the following points: First: Whereas, pursuant to § 741, the constitution of the trust established in the seventh clause cannot burden or condition the minor beneficiaries’ legal portion in any manner whatsoever, therefore the trust imposed should be limited only to the extra and free portions, leaving the remaining portion, which constitutes the legal portion, entirely *340at the disposal of the heirs. (Sections 855 and 874 of the Civil Code.) Second: As to the sixth clause, since a general or full tutorship is constituted, which is equivalent to depriving the mother of the patria potest'as in its dual declaration: over the person and property of his minor children, it being contrary to' §§ 152, 153, 163 to 167 of the Civil Code; and because the tutorship as organized cannot have three tutors to fulfill the duties' jointly, pursuant to the provisions of § 169 in relation to § 176 of the Code. Third: Protocolization Deed No. 66 executed before notary Práxedes Álvarez Leandri, on June 29, 1962, is hereby rejected as complementary document because it is contrary to art. 3 of the Mortgage Law, and to arts. 50 and 51 of the Regulations, since the protocolization of an affidavit does not have the effect of constituting such document in a public deed, according to the decision in the case of Ponce Real Estate Corporation, Edison Puerto Rico Stores, Inc. v. Registrar, appeal No. 1395. of February 7, 1963 . . . .”

An administrative appeal was filed against the preceding-note. The errors assigned are: 1) that respondent erred in failing to record the absolute ownership in favor of the trustees of the real properties constituting the hereditary-estate; 2). and likewise he erred in denying record because of the- other three reasons stated in his note.

1. The strict application of §§ 741 — “A testator cannot deprive the heir of his legal portion, except in the cases expressly fixed by law. Neither can he impose upon it any burden, condition, or substitution of any kind whatsoever, with exception of what has been prescribed with regard to the usufruct of the surviving spouse.” — 846 in fine —“Trusts constituted to the detriment or impairment of the rights of heirs at law as prescribed in this title, are hereby prohibited and are likewise null.” — and 8741 — “Nothing con*341■tained in this chapter shall be understood to repeal or modify the system of inheritance established by this title”- — of the Civil Code, 31 L.P.R.A. §§ 2367, 2553 in fine, and 2581 supports the refusal of the respondent registrar to record the properties as a whole in the name of trustees. In the presence of a similar situation — the challenge of some trusts inter vivos constituted in favor óf certain descendants with pre-terition to the sole forced heiress — we stated in Fuxá v. Torres, 85 P.R.R. 272, 275 (1962), that “Since according to § 846 of pur Civil Code any trust which impairs the rights of heirs' at law is null, it is evident that at the time of determining the legal portion of appellee, consisting of two thirds of one half of the properties transferred for the trust, the proper thing is to treat such trusts as if they had not been effected .■ . . .” The language in Belaval v. Court of Eminent Domain, 71 P.R.R. 246, 253 (1950), on which appellants seek to rely, far from being beneficial to them rather strengthens our conclusion. Although “In trusts the property which belonged to the settlor has been conveyed to the trustee, who has all rights and interest corresponding to the 'full ownership, .with the only restriction that the ■transfer is made in accordance with the mandate 'of- the settlor for the benefit of the beneficiary,” it is the best showing that actually the right of the minor beneficiaries to receive their legal portion to the extent determined by law is being limited.2 .

*342Appellants themselves argue that the transfer sought to be made in: favor of the trustees is “in fee simple and without any limitation or condition whatsoever,” since otherwise the intention of the testator and the execution of the trust would be frustrated and judicial intervention would be required every time that it were sought to encumber or alienate the property in trust. Precisely, the intent of the testator is limited by the provisions of positive law sanctioned by the invulnerability of the legal portion.

Respondent is also right in maintaining that the protoeolization of the certificate attached is not sufficient to validly credit the trustees’ acceptance. Section 872 of the Civil Code, 31 L.P.R.A. § 2579, does not authorize the recording of real property in the name of the trustee, unless there is also filed for record, along with the deed of trust the deed of acceptance. It is in accord with § 850, 31 L.P.R.A. *343§ 2557, which provides that the express acceptance must take place in the same form in which the trust is constituted. Therefore it is inferred that a public deed is required to establish the acceptance, and not an affidavit, which does not come within the category of public deed by the mere fact of its protocolization. Ponce Real Estate Corp. v. Registrar, 87 P.R.R. 202 (1963).

2. Since all that was sought was the registration of the property in the'name of the trustees, it is not necessary to consider whether the ground adduced in the note of refusal in relation to the designation of tutors and the scope of their power is correct. See, however, Mercado v. Mercado, 66 P.R.R. 764, 770-776 (1947) and Concepción v. Latoni, 51 P.R.R. 547 (1937). It is so acknowledged by appellants in stating that the sixth clause of the will does not affect in any manner whatsoever the registration of the. property requested by them.

The note appealed from will be affirmed.