MANNHEIM, Germany (AP) _ Defense lawyers at the tax evasion trial of Steffi Graf's father, Peter Graf, demanded a $10 million refund Friday, saying a lot of the money at issue was not taxable.

Graf, 58, is on trial with former family tax adviser Joachim Eckardt. They are charged with failing to declare $28 million of Steffi Graf's income between 1989-93, on which $13.1 million in taxes were due, according to authorities.

Since Peter Graf was arrested nearly 15 months ago, the family has paid the back taxes based on figures determined by investigators and tax authorities.

Eckardt's lawyer, Bernd Schneider, told the court that the investigators obviously chose to develop the charges against the defendants on the premise: ``When in doubt, work in favor of the finance office.''

``We're assuming that a maximum of $3.3 million tax was due,'' said Bernd Wipfler, a tax expert for the defense.

Graf's defense attorney Franz Salditt told the court that any punishment meted out to his client and Eckardt would have to take into consideration a much lower figure of tax evaded.

The defense comments drew an angry response from chief prosecutor Hubert Jobski, who said, ``We're here before a court and not at some weekend seminar on how to write off taxes.''

The seventh session of the trial, which began on Sept. 5, ended without a ruling on whether the charges would be altered.

On Tuesday, former Graf family adviser Horst Schmitt is to testify.

Prosecutors said that Schmitt told them in July that he had informed Steffi Graf whre he money was in 1991, saying he did not want to be blamed for her father's ambiguity on money matters.

Steffi Graf, who is to play in a tournament in Leipzig next week, was also questioned by prosecutors and told them she could not recall Schmitt telling her about the financial matters.

She said she was so busy with tennis that she left the financial management to the others. Peter Graf has also testified his daughter was innocent of any wrongdoing. She has not been charged.