U.S. Supreme Court Justice Ruth Bader Ginsburg returned to the bench Tuesday for the first time since her cancer surgery last December.

The 85-year-old justice appeared fully alert and engaged during arguments in the case Return Mail v. U.S. Postal Service, a statutory interpretation dispute involving the America Invents Act. None of the justices made any public mention of her return, customary silence for a court that is generally all business.

As was often the case before her absence, her first in more than 25 years on the bench, Ginsburg was the first justice to ask questions of Covington & Burling partner Beth Brinkmann. And neither of her questions appeared to be pre-written, because she asked about specific things that Brinkmann had just said.

“Your position is that the estoppel provision is the linchpin, you just said,” Ginsburg stated. “But your position would be the same even if there were no estoppel provision. Is that not so?”

The same familiarity she had with the case was evident with the three questions she asked of Deputy Solicitor General Malcolm Stewart, who represented the Postal Service.

The technical issues and the IP lingo that dominated the back-and-forth of the argument might otherwise have taxed the stamina of Ginsburg as well as other justices, including Clarence Thomas. Ginsburg and Thomas have at times appeared disengaged during arguments, but on Tuesday both justices were leaning forward as if they were participating in a riveting dialogue.

Ginsburg, who turns 86 next month, never missed a day on the bench during her two earlier bouts with cancer. Her long absence spawned social media rumors and calls for her to resign.

“My senior colleague, Justice John Paul Stevens, he stepped down when he was 90, so think I have about at least five more years,” Ginsburg said last July.