{dissenting). A statute should be construed to give effect to its leading idea. State v. *729Okray Produce Co., Inc., 132 Wis. 2d 145, 150, 389 N.W.2d 825, 827 (Ct. App. 1986). The legislature in enacting the sales tax law intended only to tax sales at retail. The department’s construction of the applicable statutes results in imposing an unfair and unintended tax on the sale of a small town business. An agency construction which is contrary to the legislative intent is per se unreasonable. We owe no deference to such a construction. See State ex rel. Staples v. DHSS, 136 Wis. 2d 487, 497, 402 N.W.2d 369, 375 (Ct. App. 1987) (we accept the agency’s interpretation of a statute only if it is consistent with the purpose of the statute).
Section 77.52(1), Stats. (1983-84),1 imposes a retail sales tax on sales of personal property "at retail.” Section 77.54(7) exempts from retail sales taxes the "occasional sales” of tangible personal property. Section 77.51(10)(a) defines "occasional sales” to include isolated and sporadic sales of tangible personal property where the infrequency of the sales supports the inference that the seller is not pursuing a vocation, occupation or business as a vendor of personal property. The definition further provides: "No sale of any tangible personal property or taxable service may be deemed an occasional sale if at the time of such sale the seller holds or is required to hold a seller’s permit _” Id. The obvious purpose of the latter qualification is to insure that a retail seller does not avoid the tax by claiming that a sale at retail is in fact an isolated or sporadic sale.
A seller’s permit may be held "only by persons actively operating as sellers of tangible personal property or taxable services. Any person not so operating shall forthwith surrender that person’s *730permit to the department for cancellation.” Sec. 77.52(12), Stats. In Three Lions Supper Club v. Dept. of Revenue, 72 Wis. 2d 546, 550, 241 N.W.2d 190, 192 (1976), the court rejected the department’s construction that a seller’s permit continued in effect after its surrender until cancelled by the department. The court gave the word "hold” its common meaning.
To "hold” something is to have it in one’s possession. The dictionary defines "hold” as meaning: "to retain in one’s keeping: maintain possession of: not give up or relinquish.” The Uniform Commercial Code, in another context, defines "holder” as "a person who is in possession of a document... or an instrument or an investment security ....” The word "hold” relates to possession. As used in defining "occasional sales,” it makes possession rather than cancellation the controlling factor.
Id. at 550-51, 241 N.W.2d at 192 (footnotes omitted).
Our decision today overrules Three Lions. We are not permitted to depart from supreme court precedent. State v. Lossman, 118 Wis. 2d 526, 533, 348 N.W.2d 159, 163 (1984).
The majority finds authority for overruling Three Lions in administrative regulations, Wis. Adm. Code, secs. Tax 11.13(3)(a) and (b) which require that a person holding a seller’s permit, in order to make an occasional sale, personally deliver the permit to the department before the sale or deliver the permit by a letter postmarked on the day of the sale.2 Because the *731post office in Cuba City was closed when Fiedler Foods deposited the letter containing the permit in the post office mailbox, the letter was not postmarked until several days after the sale. The department contends that therefore Fiedler Foods continued to "hold” the permit when the sale of its business closed.
Fiedler Foods did not "hold” a seller’s permit at the time it made the sale of its business assets. It no longer had the seller’s permit in its possession. It had given up and relinquished the permit. According to the supreme court, possession is the controlling factor in determining whether a person holding a seller’s permit has relinquished that permit. I do not believe the department by administrative regulation can amend the statute or overrule the supreme court.3
*732Because I believe Three Lions requires that we find that the sale of Fiedler Foods was an occasional sale, not subject to a sales tax, I dissent.
References to ch. 77, Stats., refer to the 1983-84 statutes.
The department acknowledges "the occasional seller required to hold a seller’s permit is presented with some difficulty” in complying with Wis. Adm. Code, sec. Tax 11.13(2)(a), which requires delivery of the seller’s permit to the department for cancellation prior to disposition and also complying with the *731requirement in the same section of ceasing business before delivering the permit to the department. In fact, the department seems to be playing Catch-22 games with a purchasing retailer who does not wish to terminate the operation of the business being purchased. The timing problem would be obviated if the department would follow the Three Lions decision and apply the law so that an occasional sale is not taxed if the seller has relinquished possession of the seller’s permit. A letter is surrendered when it is deposited in the United States mail. "Mailing is sufficient to satisfy the legal requirements imposed in the day-to-day conduct of business.” Mansfield v. Smith, 88 Wis. 2d 575, 588, 277 N.W.2d 740, 746 (1979). Service by mail is complete when the paper to be filed is deposited in the post office with the proper amount of postage. Schroedel Corp. v. State Highway Comm., 38 Wis. 2d 424, 428, 157 N.W.2d 562, 564 (1968). Reliance on an affidavit of deposit in the mail rather than a postmark would not leave the surrendering permit holder subject to the vagaries of the operation of the United States Postal Service.
See Aetna Life Ins. Co. v. Mitchell, 101 Wis. 2d 90, 110, 303 N.W.2d 639, 648 (1981) (rules which would require insurance companies to violate a state statute would be unreasonable).