Here's the 1996 Senate Report explaining the 1990 treaty between the Swiss and the U.S. It begins:

On November 14, 1990, the President signed an extradition treaty with Switzerland. The Treaty was transmitted to the Senate for its advice and consent to ratification on June 12, 1995.

Section VII contains an explanation of the treaty's provisions. First, it applies to people who have been found guilty but not been sentenced. To make that clear, it avoids using the word "convicted."

Article 1--Obligation to extradite...formally obligates each Contracting Party to extradite to the other pursuant to the provisions of the Treaty persons charged with or found guilty of an extraditable offense, or subject to a detention order in the Requesting State. The term ``found guilty'' was used instead of ``convicted'' because in Switzerland, a person is not considered convicted until a sentence has been imposed, whereas in the United States, a sentence is ordinarily not imposed on a convicted person until after a presentence report has been prepared and reviewed. The negotiators intended to make it clear that the Treaty applies to persons who have been adjudged guilty but flee prior to sentencing.

Article 22 says the treaty applies to offenses committed before its enactment.

Article 2 addresses what constitutes an extraditable offense:

Article 2, sometimes referred to as a dual criminality clause, defines extraditable offenses as offenses punishable in both contracting states by prison terms of more than one year.

....[A]n offense is extraditable if it is punishable under the laws of both parties by a prison term of at least one year....If the extradition request involves a fugitive, it shall be granted only if the remaining sentence to be served is more than six months. (my emphasis)

...In order to ensure that extradition is not requested for minor offenses, paragraph 1 requires that if the person has already been sentenced, the person must have at least six months of that sentence still to serve.

The Swiss Federal Office Of Justice explains it a little differently:

Old extradition treaties contain a list of offences for which provision for extradition is made. More modern treaties, however, such as the European Convention on Extradition, provide for extradition if the alleged offence is punishable by a custodial sentence of a certain minimum duration (one year), or if a sentence of a certain minimum duration (four months) has been imposed.

Here are the Swiss Extradition Guidelines.

Further, it appears since the extradition request does not seek extradition for a new charge of fleeing to avoid sentencing, and no such charges are pending against Polanski, such an offense, even if it could be added in the U.S. now, cannot be considered by the Swiss.

Under the principle of speciality, the extradited person may be prosecuted, held in custody or extradited on to a third state only for those criminal offices that were committed prior to their extradition and on the basis of which the extradition was approved. Once extradition has taken place, the requested state may nonetheless approve further prosecution on the basis of a subsequent application.

So here's the rub: At yesterday's hearing, Judge Espinoza said:

“Nothing precludes the possibility that Judge Rittenband’s promise will someday be enforced,” he said. And, he added: “I don’t disagree that the intended sentence was” the time Mr. Polanski already spent in a state prison under psychiatric evaluation. (my emphasis)

According to the LA Times, Espinoza was even more specific:

Espinoza appeared to agree, saying of the 42 days Polanski spent in the state prison in Chino, "It's clear to me that was the intended sentence."

But, he added, since the director skipped town on the eve of the hearing, sentencing was never formally imposed and the case remained open.

The Swiss may have to decide whether Roman, having already served 42 days of a promised and intended but not fully imposed 90 day sentence, before becoming a fugitive, fits within the section that allows extradition "only if the remaining sentence to be served is more than six months." If they decide he doesn't, it can and should refuse extradition.

The Swiss were hoping for guidance from yesterday's court hearing. If they don't feel they got it, how will they decide? Will they look to other parts of the record? For example, in addition to the Judge's comments yesterday, the California appeals court in its opinion noted:

If a hearing had been requested on the record and granted, by Polanski’s account at least three people could have testified at the sentencing hearing to the trial court’s agreement that the diagnostic study would constitute Polanski’s entire punishment: Dalton, Gunson, and probation officer Gold.

Now, with the victim's lawyer's filing this week, there are four affidavits on file all stating the Judge expressly promised not to exceed the 90 sentence for evaluation.

In a new revelation, Silver wrote in his legal filing that he witnessed Rittenband say in his chambers that no other incarceration would be imposed, only to then renege on his promise and threaten to send Polanski to an indeterminate prison sentence. Polanski fled the country soon after.

If the Swiss consider, in combination: Judge Espinoza's statement yesterday that it's clear the original sentencing judge only intended a 90 day sentence; the four sworn statements of the former case prosecutor, the probation officer, Roman's lawyer and the victim's lawyer, all attesting that the Judge promised no more than 90 days if Roman went to do the psych evaluation; that Roman, relying on that representation, agreed, and the Judge then imposed the psych evaluation sentence; that Roman complied with his end by going into prison for the evaluation and when he came out, there were less than four or six months remaining of the promised and intended 90 day sentence, will they decide the U.S. has not met the legal requirements for extradition?

More on this aspect at yesterday's hearing:

In court documents, Polanski's attorneys said the late Superior Court Judge Laurence J. Rittenband sentenced the director in 1978 to a diagnostic study at a California prison where he served 42 days.

Although the judge told attorneys that would be Polanski's full sentence, he later indicated he was going to renege on the bargain and give him a harsher sentence at a scheduled hearing. Polanski fled to France and has been a fugitive ever since. His attorneys said the judge's promise is binding and Polanski has served his full sentence.

Judge Espinoza agreed with the 90 day intent, but expressed his belief the sentence hadn't actually been imposed:

Espinoza added another twist in his remarks from the bench by saying he believes Rittenband originally intended to sentence Polanski to a maximum 90-day period of incarceration for the diagnostic study but never officially imposed the penalty in court.

The Judge's position doesn't seem reasonable considering Polanksi appeared for sentencing and was ordered to prison where he spent 42 days. Also, when Romanski pleaaded guilty, the judge said he'd make his final decision after reading and considering the evaluation report and probation report and hearing from counsel. All of which he refused to do.

Instead, after the Judge had imposed and Polanski had served the diagnostic portion of the sentence, the Judge scheduled another sentencing hearing. And days before the hearing, he told the prosecutor and Roman's lawyer he had changed his mind, he was going to impose additional time. So the judge at least partially imposed the sentence, and Roman had served it.

The way I see it, or at least the argument I'd make, is that since the sentence had partially been served, the legal question to be decided by the Swiss is not what could he have been sentenced to, but how much time remained to be served. Since everyone, including the current Judge, agrees the original Judge intended to and promised to impose no more than 90 days, and Roman served 42 of them, there is less than four or six months remaining on his sentence and the request doesn't comply with the U.S.- Swiss treaty or Swiss law.