The plaintiffs filed a complaint in the Supreme Judicial Court for Suffolk County seeking relief in the nature of certiorari and mandamus respectively against the Attorney General and the Secretary of the Commonwealth in their official capacities. The plaintiffs challenge the Attorney General’s certification of an initiative petition pursuant to art. 48 of the Amendments to the Constitution of the Commonwealth. Art. 48, The Initiative, II, § 3.3 The petition, entitled “The Stop Nuclear Waste Act” by its proponents, would, after July 4,1989, prohibit “generation of electric power by commercial nuclear power plants in the Commonwealth by means which result in the production of nuclear waste.” The plaintiffs also seek to prevent the Secretary of the Commonwealth from having the initiative measure placed on the ballot in the upcoming State election. See art. 48, The Initiative, IV, § 5. The single justice reserved and reported the case for consideration by the full court on the parties’ motion.
The plaintiffs maintain that the petition, if enacted, would constitute a “taking” of the property of plaintiff Yankee Atomic Electric Company and one other electric utility within the Commonwealth, and that the Attorney General is therefore required under art. 48 to decline to certify the initiative petition for a place upon the ballot.
*205This is the second decision and opinion of this court relating to this controversy. On July 7, 1988, this court’s opinion in Yankee Atomic Elec. Co. v. Secretary of the Commonwealth, 402 Mass. 750 (1988) (Yankee One), ordered the Attorney General to make an examination of the facts relating to the initiative petition. The court stated that the Attorney General’s duty under the Massachusetts Constitution, art. 48, The Initiative, is to certify proposed initiative petitions, and this duty requires the Attorney General to determine, among other things, whether the petition contains matter excluded from the initiative process by art. 48, The Initiative, II, § 2.4 Among the matters thus excluded from the initiative are propositions inconsistent with the right to receive compensation for private property appropriated to public use. In response to the plaintiffs’ argument that the Attorney General is required to make a factual investigation and analysis in order to determine whether the proposed initiative should be excluded from the ballot, the court stated that the factual examination required of the Attorney General is limited to matters implicit in the language of the petition and to matters of which the Attorney General may properly take official notice. The court, in defining official notice, stated: “Factual matters which are ‘indisputably true’ are subject to judicial notice; these include ‘[mjatters of common knowledge or observation within the community.’
. . . Official notice includes matters subject to judicial notice, as well as additional items of which an agency official may take notice due to the agency’s established familiarity with and expertise regarding a particular subject area.” (Citations omitted). Yankee One, supra at 759 n.7.
*206In Yankee One, in ordering that the Attorney General must make the limited factual examination as defined by the court, we further stated that if it is the Attorney General’s decision to affirm his certification after factual examination, the certification shall be considered to be valid ab initio. Id. at 759-760. We also directed that the county court was to retain jurisdiction of this case, and that the single justice in his discretion was to enter orders to expedite the proceedings. Id. at 760. Subsequently, pursuant to a time schedule ordered by the single justice by agreement of the parties, the Attorney General on July 19, 1988, filed in the county court a copy of his letter of that date to the Secretary of the Commonwealth in which the Attorney General affirmed his certification of the petition. Subsequently, the single justice reported the case back to the full court without decision.* *** 5
The Attorney General in his letter of July 19, 1988, stated: “In reexamining the validity of the petition I have considered those facts implied by the petition’s language and those officially noticeable. Id. at 759. I have also reviewed facts proffered and arguments submitted by the proponents and opponents of the petition.” He then stated all the facts which he had considered in affirming his original decision that the petition does not establish, on its face, that it effects a regulatory taking.6
*207In assessing the Attorney General’s conclusion that, on consideration of the pertinent facts, the petition does not, on its face, establish a regulatory taking, we undertake de novo review. Massachusetts Teachers Ass’n v. Secretary of the Commonwealth, 384 Mass. 209, 230 n.18 (1981). See, e.g., Bowe v. Secretary of the Commonwealth, 320 Mass. 230, 248-253 (1946) (court engages in de novo review in considering whether petition contains excluded matter); Horton v. Attorney Gen., 269 Mass. 503, 511-512 (1929) (same). Similarly, in considering what facts are implicit in the petition’s language or are subject to judicial notice, see Yankee One, supra at 759 & n.7, we are not bound by the Attorney General’s determinations. However, in assessing the extent of the facts subject to his official notice, see id., we will defer to the Attorney General’s reasonable determinations. See Massachusetts Teachers Ass’n, supra at 230. Cf. Beth Israel Hosp. Ass’n v. Board of Registration in Medicine, 401 Mass. 172, 176 (1987) (“all presumptions are in favor of the validity of agency action . . . [and] agencies have leeway in interpreting statutes they enforce”).
*208Guided by our description in Yankee One of the limited factual examination required of the Attorney General, we first consider whether there are facts implicit in the petition’s language or facts subject to judicial notice, i.e., indisputable facts or matters of common knowledge, which the Attorney General should have considered and did not. In our view there are no such facts. The Attorney General’s summary of the facts he considered, supra note 6, contains all the facts which we would consider to be implicit in the petition’s language and subject to judicial notice.
Next we determine whether there are further facts of which, in accordance with our directions to him in Yankee One, supra at 759 & n.7, the Attorney General should have taken official notice “due to [his] established familiarity with and expertise regarding a particular subject area.” Beyond question, the person best qualified to determine the extent of his expert knowledge is the Attorney General. In that regard we shall not lightly substitute our view of what are the officially noticeable facts for that of the Attorney General. See Massachusetts Teachers Ass’n, supra at 230. Cf. Beth Israel Hosp. Ass’n, supra, and cases cited. Our review of the summary of the facts he considered, supra note 6, leads us to conclude that the Attorney General did not arbitrarily omit facts apparently subject to his official notice. Accordingly, we accept as reasonable the Attorney General’s determination of the facts he has considered in affirming his certification of the petition.
We next consider whether the facts recognized by the Attorney General preclude him under art. 48, as a matter of law, from certifying the petition. Here we look particularly at the Attorney General’s finding that “I infer from [the petition’s] prohibition that it would prevent Yankee and Boston Edison from generating any electricity by use of their nuclear reactors in their current forms after July 4, 1989.” Supra note 6. Do the facts as properly found compel a conclusion that this petition proposes legislation which would bring about a taking of private property without compensation? We think not, and in so concluding we look to the legal principles which have controlled in cases similar to the case before us.
*209Our review of these principles reveals issues (1) which are relevant to the question whether a taking would ensue from the proposed legislation, and (2) which have not been, and should not be, determined through the Attorney General’s limited examination of the facts at this time. The petition proposes not a permanent physical occupation or confiscation of property, see Loretto v. Teleprompter Manhattan CATV Corp., 458 U.S. 419, 426 (1982), but instead a regulation of use of property. As such the question is whether the “regulation goes too far.” Pennsylvania Coal Co. v. Mahon, 260 U.S. 393, 415 (1922). Answering this question involves regulatory takings analysis which is peculiarly fact dependent, involving “essentially ad hoc, factual inquiries.” Penn Cent. Transp. Co. v. New York City, 438 U.S. 104, 124(1978). See Turnpike Realty Co. v. Dedham, 362 Mass. 221, 236 (1972), cert. denied, 409 U.S. 1108 (1973). We conclude that at least some of the relevant inquiries which may arise in the ultimate determination whether a taking of property has occurred will involve the kind of lengthy factual determinations which art. 48 does not require or allow to the Attorney General at this time.
In his letter of July 19, 1988, to the Secretary of the Commonwealth, affirming his certification, the Attorney General describes a number of these factual inquiries, and asserts, that they are relevant to the regulatory takings analysis.7 We think *210that this assertion is well made in that the existence of the undetermined factual issues raised, supra note 7, leads to reasonable, not frivolous, contentions that the petition does not necessarily effect a regulatory taking. This is so because the presently undetermined factual issues pointed to by the Attorney General have been held to be relevant to regulatory takings analysis. Thus, the issue of residual use is relevant, see, e.g., Penn Cent. Transp. Co., supra at 131; MacNeil v. Avon, 386 Mass. 339, 341 (1982); Lovequist v. Conservation Comm’n of Dennis, 379 Mass. 7, 10 (1979), as is the determination of the diminution in value of the regulated property. See Goldblatt v. Hempstead, 369 U.S. 590, 594 (1962). See also Hadacheck v. Sebastian, 239 U.S. 394 (1915) (no regulatory taking despite substantial diminution in value); Turnpike Realty Co., supra (same).
The possibility of compensation through the rate setting process cited by the Attorney General affects the “takings” analysis in this case in a manner similar to the possibility that an appropriate board might grant a special permit affects the takings analysis in a case where a zoning by-law is challenged. See MacGibbon v. Board of Appeals of Duxbury, 356 Mass. 635, 641 (1970). In both instances the determination whether a taking is present depends, in part, on a factual inquiry regarding possible agency action. The possibility of compensation through the rate setting process also has an impact on the question of the degree of interference with investment-backed expectations caused by the petition. See Penn Central, supra at 124.
In sum, the facts implicit in the petition’s language taken with those susceptible to the Attorney General’s official notice *211do not establish that the petition effects a regulatory taking.8 In this circumstance, it was reasonable and proper for the Attorney General to affirm the petition’s certification. This result is consistent with the firmly established principle that art. 48 is to be construed to support the people’s prerogative to initiate and adopt laws. See Buckley v. Secretary of the Commonwealth, 371 Mass. 195, 199, 202-203 (1976); 2 Debates in the Massachusetts Constitutional Convention, 1917-1918, at 728 (191.8) (when certifying petitions as to proper form, Attorney General is not to be a censor; people should be allowed to speak and act freely through the initiative process). In reaching this result we are, of course, not reaching or impliedly commenting as to the wisdom of the proposed legislation.
We affirm the Attorney General’s certification of the initiative petition. The certification was valid ab initio. The Secretary of the Commonwealth shall take the appropriate steps to have *212the measure placed on the ballot in the upcoming State elections.9 Rescript is to enter forthwith.10
So ordered.
All references are to art. 48 as amended by art. 74, by art. 81, and by art. 108 of the Amendments to the Constitution of the Commonwealth.
Article 48, The Initiative, II, § 2, provides in relevant part as follows:
“Excluded Matters ... No proposition inconsistent with any one of the following rights of the individual, as at present declared in the declaration of rights, shall be the subject of an initiative or referendum petition: The right to receive compensation for private property appropriated to public use; the right of access to and protection in courts of justice; the right of trial by jury; protection from unreasonable search, unreasonable bail and the law martial; freedom of the press; freedom of speech; freedom of elections; and the right of peaceable assembly.”
Article 48, The Initiative, II, § 3, provides in relevant part as follows:
*206“Mode of Originating. Such petition shall first be signed by ten qualified voters of the commonwealth and shall be submitted to the attorney-general not later than the first Wednesday of the August before the assembling of the general court into which it is to be introduced, and if he shall certify that the measure and the title thereof are in proper form for submission to the people, and that the measure is not, either affirmatively or negatively, substantially the same as any measure which has been qualified for submission or submitted to the people at either of the two preceding biennial state elections, and that it contains only subjects not excluded from the popular initiative and which are related or which are mutually dependent, it may then be filed with the secretary of the commonwealth.”
The parties filed supplemental briefs with the full court on or before August 3, 1988.
The Attorney General’s summary of the facts was as follows: “Yankee Atomic Electric Company (Yankee) and Boston Edison Company (Boston Edison) own and operate the only two commercial nuclear reactors in the
*207Commonwealth. Yankee’s plant is located in Rowe, Massachusetts. Boston Edison’s plant is located in Plymouth, Massachusetts. According to the company and local real estate records, Yankee’s plant is situated on approximately 2,200 acres of land in Rowe.
“Yankee and Boston Edison operate their plants under licenses granted to them by the United States government. Yankee’s license to operate the plant in Rowe was issued by the Atomic Energy Commission in 1957. Boston Edison’s license to operate the plant in Plymouth was issued in 1972 by the Atomic Energy Commission. The terms of the licenses include, inter alia, the period of time for which they are issued. Federal law establishes requirements for the operation of the plants. Yankee and Boston Edison invested money to build the plants, and the companies sell or have sold electricity generated by the plants. Contracts for the sale of this electricity are subject to review by appropriate regulatory agencies.
“The petition does not, either facially or implicitly, exercise the power of eminent domain or mandate a physical taking or invasion of private property. The apparent impact of the petition, however, would be to prohibit after July 4, 1989, the generation of electricity by these two reactors ‘by means which result in the production of nuclear waste.’ I infer from this prohibition that it would prevent Yankee and Boston Edison from generating any electricity by use of their nuclear reactors in their current forms after July 4, 1989.”
The Attorney General wrote as follows: “Nothing in the petition, how- . ever, restricts alternative uses of the property that might be affected by the petition. The proponents and opponents of the petition dispute the possible alternative uses of the affected property. For example, the proponents assert that the property could be converted to another power source, used for a low-level waste repository, or used for other commercial purposes. The opponents dispute the availability of these proposed alternative uses. In my view, these issues of ‘residual use’ present questions of fact beyond the scope of my review. Certain of the disputed residual uses implicate future regulatory proceedings, such as licensing proceedings, the outcomes of which are not determinable at this time. In such circumstances I cannot conclude that the petition is ‘inconsistent’ with the asserted ‘right to receive compensation for private property appropriated to public use’ simply because one use of the property of the companies is foreclosed.
“Similarly , the actual values of the Yankee and Boston Edison properties before and after the effective date of the petition are not facts susceptible to official notice. Resolution of such questions would require me to decide, *210among other things, disputable facts such as the actual net values of the properties before and after the effective date of the petition, and the extent to which the plants’ owners may be permitted to recover their investments in the idled plants through existing regulatory processes. There are subsidiary facts, relevant to the actual values of the plants, that are indisputable. For example, I have taken official notice of past real estate tax assessments of the Yankee property by the Town of Rowe. However, the values of the properties in question remain ultimate facts not subject to official notice. ”
The plaintiffs’ argument that, on the facts as established by the Attorney General, the petition effects a regulatory taking improperly divides the utilities’ property into discrete segments and focuses on the petition’s impact on one of these segments (the reactor) rather than considering the petition’s interference with the utilities’ property rights as to the affected sites as a whole. See Keystone Bituminous Coal Ass’n v. DeBenedictis, 480 U.S. 470, 495-498 (1987). Further, even if such dissection of the utilities’ property is appropriate, possible other uses of the reactor (e.g., nuclear waste storage site), and the possibility of compensation through the rate setting process of the cost of conversion from nuclear to fossil fuel generation of electricity, or for the loss of generating capacity, indicates that the plaintiffs’ argument is not determinative.
Should the measure be adopted by the people, the plaintiffs are free to pursue, in appropriate fashion, any and all challenges, aside from those decided in this proceeding, they may have to the petition’s validity. See Bowe v. Secretary of the Commonwealth, supra at 243-248; Horton v. Attorney Gen., supra at 513-515. In ruling that the Attorney General’s certification of the petition was proper, we do not preclude a determination, on appropriate proof and following the necessary factual resolutions, that the petition effects a regulatory taking as applied to particular property. We merely hold that, on the limited findings of fact permitted to the Attorney General at this time, the petition does not necessarily involve such a taking.
Two Justices of the court found it necessary to recuse themselves from participating, and thus this matter was left to five Justices for decision. Although only three of the Justices concur in the result supra, the full panel is in agreement that judgment shall enter as above. See G. L. c. 211, § 2 (1986 ed.) (“four justices . . . constitute a quorum to decide all matters required to be heard by [the court]”). See also Commonwealth v. Geraway, 364 Mass. 168, 186 (1973) (decision of three Justices disposes of case).