WASHINGTON (Reuters) - U.S. Supreme Court Justice Ruth Bader Ginsburg, returning to the bench for the first time since undergoing lung cancer surgery in December, jumped right into the fray on Tuesday, posing the first question in oral arguments as is her custom.

FILE PHOTO: U.S. Supreme Court Justice Ruth Bader Ginsburg is seen during a group portrait session for the new full court at the Supreme Court in Washington, U.S., November 30, 2018. REUTERS/Jim Young/File Photo

The diminutive liberal justice, who will turn 86 next month, was steady on her feet as she entered the ornate courtroom before participating in the hour-long argument in a patent dispute pitting an Alabama company against the U.S. Postal Service.

Wearing one of her signature decorative collars, the black-robed Ginsburg appeared attentive throughout the argument, asking in a clear voice several technical questions. Her return to the bench seemed unremarkable to the eight other justices, none of whom made mention of it.

She stood with the other justices as the court marshal called the court to order, then took her usual seat to the right of Chief Justice John Roberts.

Ginsburg, who joined the court in 1993 and was the subject of both a documentary film and a Hollywood biographical movie last year, has made a trademark of becoming the first questioner in most cases before the nation’s highest court.

She underwent a surgical procedure called a pulmonary lobectomy on Dec. 21 at Memorial Sloan Kettering Cancer Center in New York to remove two cancerous nodules in her left lung, her latest bout with cancer. She was released from the hospital on Dec. 25.

Ginsburg returned to the court on Friday for the first time since the surgery to take part in the justices’ private conference. Last month, the court said Ginsburg’s recovery was on track and there was no evidence of remaining disease.

Ginsburg missed oral arguments in January for the first time in her lengthy career on the court, fueling speculation about her ability to continue in the job. As the oldest justice, she is closely watched for any signs of deteriorating health.

She is one of four liberal justices on a court with a 5-4 conservative majority.

Tuesday’s case involved a small company’s claim that the U.S. Postal Service infringed its patented mail-processing system and then improperly used a U.S. Patent and Trademark Office tribunal to cancel the patent.

The company, Return Mail, Inc, argued that since the Postal Service, a self-supporting independent federal agency, cannot be sued in the same way as private companies, it should not be eligible to ask the patent office to review a patent’s validity like private companies can.

Most of the justices, including Ginsburg, asked tough questions of both sides.

At one point, Ginsburg asked Deputy Solicitor General Malcolm Stewart, the Trump administration lawyer who was defending the Postal Service, whether allowing the government access to patent reviews gives it “two bites of the apple” since it is not subject to the same constraints as private parties are when defending against infringement suits.

Though she worked from home during her absence from the court, Ginsburg attended a Feb. 4 concert in Washington titled “Notorious RBG in Song.” She is viewed as something of a cult figure by U.S. liberals, known by that nickname after the late rapper Notorious BIG.