The Government seeks writs of mandamus directing respondent judge to vacate his order dismissing indictments in cases pending before him in the District Court of the United States for the Central District of California. [United States of America v. Linetsky, et al., No. 7145; United States of America v. Carlo, et al., No. 7142].

FACTS

On December 22, 1970, a 36-count indictment was returned against Linetsky and others charging, in substance, one or more of the defendants, real parties in interest here, with violations of Title 18 U.S.C. § 1461 , in knowingly depositing obscene advertisements in the United States Mail for carriage and delivery. Each defendant pled not guilty. Also on December 22, 1970, an eleven-count indictment was returned against defendant Carlo and others charging, in substance, the same kind of violations of the same statute on obscenity. Each defendant pled not guilty.

Later, the parties in each case stipulated, for the purpose of minimizing discovery, that the materials that appeared in the stipulation were copies of the materials underlying the indictment.

The Linetsky case was consolidated with the Carlo case for the purpose of hearing on defendants’ motion to dismiss, made pursuant to Rule 12, F.R. Crim.P. A hearing on the motions to dismiss was continued to August 5, 1971. On July 20, 1971, the Government filed, in each case, a memorandum in opposition to the hearings on the respective motions to dismiss. This opposition contained the following statement:

On August 5, 1971, despite the opposition of the Government, the trial judge held hearings on defendants’ motions to dismiss and, over the opposition of the Government, allowed defendants to introduce into evidence the stipulated materials together with certain materials (magazines and a film) previously adjudicated as protected under the First Amendment, in unrelated obscenity prosecutions. The Government, solely for the purpose of apprising the judge of its position and to protect its interest in the prosecution, offered three advertisements from the case of Miller v. United States, 9 Cir., 1970. 431 F.2d 655 [CA 9, 1970]. The trial judge then made a pre-trial determination that the materials, which formed the basis of both of the indictments, were not obscene as a matter of law and dismissed both indictments.

Issues Presented

(1) Did the Government have a right of appeal to either the Circuit or the Supreme Court?

(2) Did the judge’s action place the defendants in jeopardy? If so, should the writ issue ?

As will be seen, the first question also involves the second question, and an affirmative answer to the second question also provides an answer to the first question.

1. Right to appeal.

Real parties in interest argue that the Government could have appealed, but did not, and that therefore the writ does not lie. We withheld decision in this litiga *761 tion pending the outcome in United States v. Weller, 9 Cir., 1972, 466 F.2d 1279 , which was to follow the Supreme Court’s remand in United States v. Weller, 1971, 401 U.S. 254 , 91 S.Ct. 602 , 28 L.Ed.2d 26 .

We need not decide, however, whether the two Weller cases preclude an appeal by the Government here. The Criminal Appeals Act, as amended, 18 U.S.C. § 3731 , permits the Government to appeal in certain cases, “except that no appeal shall lie where the double jeopardy clause of the United States Constitution prohibits further prosecution,” or “after the defendant has been put in jeopardy.” Because we are of the opinion that the real parties in interest have been put in jeopardy, we hold that the Government has no right to appeal.

The law as to when a defendant has been put in jeopardy — when jeopardy “attaches” — is technical, but not so technical as to permit a holding in this case that jeopardy has not attached. The general rule is stated in McCarthy v. Zerbst, 10 Cir., 1936, 85 F.2d 640 , 642:

See also Clawans v. Rives, 1939, 70 U.S. App.D.C. 107, 104 F.2d 240, 242 .

These cases meet the foregoing criteria. In each, the defendants had been arraigned on valid indictments and had pled. The court then “heard” evidence going to the general issue — whether the matter mailed was “obscene,” a necessary element of the offense. Having considered the evidence, the court ruled, “as a matter of law,” that the matter was not obscene. The court did not hold that the indictments were defective. On their faces, they were valid. What the court held, in substance, was that the defendants before it were not guilty. Surely, a court is “hearing” the evidence just as much when it receives written evidence as when it hears oral testimony of a witness. Many cases are tried solely on written evidence, sometimes on a stipulation of facts, sometimes on a transcript of a preliminary hearing or of a preliminary motion, such as a motion to suppress, sometimes upon evidentiary exhibits alone. A prime example is Selective Service cases, which are frequently tried upon the Selective Service file alone. We have held that a trial of this type places the defendant in jeopardy. United States v. McFadden, 9 Cir., 1972, 462 F.2d 484 .

In this case the evidence was received and the court’s decision was made in a proceeding denominated a motion to dismiss rather than in a “trial.” But that fact is not conclusive. This was made clear long ago in United States v. Oppenheimer, 1916, 242 U.S. 85 , 37 S.Ct. 68 , 61 L.Ed. 161 . There, an indictment had been dismissed on the ground that the charge was barred by the statute of limitations, a view of the statute of limitations later held erroneous by the Supreme Court in another case. A new indictment was procured, defendant’s plea of double jeopardy was overruled, and he was convicted. On appeal, the conviction was reversed. Speaking for a unanimous Court, Mr. Justice Holmes said:

See also Dear Wing Jung v. United States, 9 Cir., 1962, 312 F.2d 73, 74 .

The district judge did not think that he was holding a trial; he believed that jeopardy had not attached. That was equally true in McFadden, supra. Moreover in Oppenheimer, supra, there had been no trial at all in the conventional sense, but merely a motion to dismiss, apparently without the reception of any evidence. What was controlling was that the judge had rendered a decision for the defendant “as a matter of substantive law.” It may be that in Oppenheimer the Court was applying res judi-cata or collateral estoppel rather than, or as much as, double jeopardy, although that is by no means clear. The distinction, if any, is immaterial. In Ashe v. Swenson, 1970, 397 U.S. 436, 445 , 90 S.Ct. 1187 , 25 L.Ed.2d 469 , the Court held that the principle of collateral estoppel is embodied in the Fifth Amendment guarantee against double jeopardy. See also Simpson v. Florida, 1971, 403 U.S. 384, 385 , 91 S.Ct. 1801 , 29 L.Ed.2d 549 . McFadden rests squarely on jeopardy. There, as here, the court received evidence going to the general issue, and it rendered a decision which was, in substance though not in form, a finding that the defendants were not guilty as a matter of law.

It may also be that the trial judge’s procedure was unauthorized and improper. Perhaps, had the Government applied to us for relief before the judge heard the motion and received evidence in support of it, we could have granted relief under the All-Writs Act. But the Government did not do so, and the trial judge did proceed to receive evidence and to rule. The decision that was held to prevent a second trial in Oppenheimer, supra was erroneous. The decision that was held to be a bar in McFadden, supra, had been vacated by the Supreme Court. In Fong Foo v. United States, 1962, 369 U.S. 141 , 82 S. Ct. 671 , 7 L.Ed.2d 629 , the Court assumed, as the Court of Appeals had held, that the first decision was “based upon an egregiously erroneous foundation,” but held, nevertheless, that it constituted former jeopardy.

If in this case the judge had proceeded to trial in the usual way, with or *763 without a jury, and if the Government had then, as its first move, offered in evidence the stipulated exhibits, and if the judge had then ruled, as a matter of law, that those exhibits were not obscene, and had entered a judgment of acquittal, there could be no doubt that the defendants had been placed in jeopardy, however erroneous, the acquittal might be. Fong Foo v. United States, supra. See also Green v. United States, 1957, 355 U.S. 184, 188 , 78 S.Ct. 221 , 2 L.Ed. 2d 199 . Such a procedure would have deprived the Government of its asserted right to have the jury decide the issue of obscenity just as much as did the decision in this case. That is, in substance, what happened in this case. And únder Oppenheimer and McFadden, supra, it is substance, not form, that governs.

It is of course true that many preliminary proceedings and motions, where evidence is received, do not amount to jeopardy. Thus, a preliminary hearing does not put the defendant in jeopardy. Collins v. Loisel, 1923, 262 U.S. 426, 429 , 43 S.Ct. 618 , 67 L.Ed. 1062 ; United States v. Malfetti, 3 Cir., 1954, 213 F.2d 728, 729-730 ; United States v. Grimes, 5 Cir., 1970, 426 F.2d 706, 708 ; Draper v. Rhay, 9 Cir., 1966, 358 F.2d 304 , affirming, E.D.Wash., 1964, 242 F.Supp. 829, 833-834 . So also, a motion to suppress evidence, in which testimony is taken from both sides, does not place the defendant in jeopardy. United States v. Williams, 4 Cir., 1955, 227 F.2d 149, 152 . Double jeopardy does not occur in such cases because the court is not deciding the general issue — guilt vel non. In contrast, in the present case, guilt is precisely the issue that the court decided; it held that the material received in evidence was not obscene, and dismissed the cases. In substance, though not in form, that was an acquittal.

2. Should the writ issue?

There being no right to appeal, the remaining question is, should the writ issue? We think not. Issuance is discretionary. Here, to issue the writ would accomplish nothing. Having set aside his order, the district judge would have to dismiss again on the ground of double jeopardy. We recognize that former jeopardy is usually raised by plea; it is a defense that can be waived. But we see not the slightest possibility of waiver here. 1 We *764 should not waste judicial manpower by-requiring further and, in our view, meaningless further proceedings in the trial court. We should exercise our discretion to deny mandamus. See Duncan Townsite Co. v. Lane, 1917, 245 U.S. 308, 311-312 , 38 S.Ct. 99 , 62 L.Ed. 309 ; United States v. Carter, 9 Cir., 1959, 270 F.2d 521, 524 ; In re Welch Mfg. Co., 1 Cir., 1913, 201 F. 519 . That is precisely the result reached by the Supreme Court in Fong Foo v. United States, supra.

In United States v. Gray, 9 Cir., 1971, 448 F.2d 164 , we declined to consider whether double jeopardy was involved, leaving the question to the district court. Here, however, the situation is different. Real parties in interest urge that the writ should be denied because the Government could have appealed and did not do so. That contention puts in issue, before us, the jeopardy question because of the language of the Criminal Appeals Act. Because we must decide the question, there is nothing to be gained by requiring the district judge to decide it again.

Writ denied.

. In the entire record of the proceeding before tiie district judge that is before us, there is but one reference to the subject of double jeopardy. At the conclusion of the hearing, when the judge made his order, he also gave a brief oral discourse on tiie advantages of the procedure that he was using. In the course of doing so, lie said: “This procedure preserves the government's right to appeal since jeopardy lias not attached; . . a . ” Neither counsel for the government nor counsel for the real parties in interest made any comment about this statement. Whether counsel for the defendants then believed that the statement was correct cannot be ascertained from tiie record. Certainly, however, there was no express waiver of the plea of double jeopardy on their part. What they got, as we have shown, was a truncated trial on the merits before the judge. Whether they believed that such a trial caused jeopardy to attach is immaterial.

Before this court memoranda were filed in opposition to tiie petition by two sets of real parties in interest. One of them, on behalf of Carlo, contains no reference whatever to double jeopardy. In the other, on behalf of the Linetsky defendants, in arguing that the government had a right to appeal, counsel said this: “Since the case at bar had not been to trial — no jury was sworn, no witnesses-called — it is clear that defendants were not put in jeopardy.” This is the-sole reference to the subject before this court. It is nothing more than an argument based upon a mistaken view of the law. We leave it to the reader to decide how vehement a disclaimer or how resolute a position it can be said to be. We do not think that a mistaken legal argument before this court in opposition - to the writ is any more a waiver by counsel of a defense to which his clients are entitled than is a failure to disagree with a statement on the subject volunteered by the district judge.

We note, too, that counsel for the Linet-sky defendants from whose memorandum we have quoted, urged at oral argument that the ruling of the district judge was *764 on the merits, so that jeopardy had attached, under the decision of the Seventh Circuit in United States v. Ponto, 1971, 454 F.2d 647, 653 , id., in banc, 1971, 454 F.2d 657, 663-664 , and fn. 10, and that therefore the writ should not issue.