The UK Supreme Court began hearing legal arguments on Tuesday about whether Prime Minister Boris Johnson's decision to suspend parliament in the run-up to Brexit was illegal.
Here is some information about on the three-day hearing and some key quotes.
Why a Court Hearing?
Britain is due to leave the European Union on October 31. Parliament, where Johnson does not have a majority, is divided over how and whether that should happen in the absence of a divorce deal with the 27 other members of the bloc.
Johnson announced on Aug. 28 that he had asked Queen Elizabeth to suspend parliament for five weeks until Oct. 14, saying the shutdown was necessary to allow him to introduce a new legislative agenda. Opponents say the reason was to prevent scrutiny of and challenges to his Brexit plans by parliament.
Who is Involved?
Two separate legal cases about the dispute, handled by lower courts, resulted in conflicting rulings. The Supreme Court has joined them together.
In one case, businesswoman and anti-Brexit activist Gina Miller asserted that the suspension of parliament was an abuse of power by Johnson, and lost.
In the other case, Scottish member of parliament Joanna Cherry put forward similar arguments, and won.
The Supreme Court will hear arguments from lawyers for Miller, Cherry and the government, as well as additional submissions from a small number of interested parties.
The case will be heard by all 11 Supreme Court justices, led by their president, Lady Brenda Hale.
The Supreme Court's ruling will be final.
Tuesday: Lawyers for Miller, against the prime minister. Then lawyers for the government, against Cherry.
Wednesday: Lawyers for the prime minister, against Miller. Then lawyers for Cherry, against the government.
Thursday: Lawyers for the interested parties. Then final submissions by lawyers for the government and for Miller.
When Will a Ruling Come?
The earliest would be late on Thursday, but that is unlikely. It is much more likely to come in the following days.
Lady Hale, President of Supreme Court, in Her Introduction:
"That this is a serious and difficult question of law is amply demonstrated by the fact that three senior judges in Scotland have reached a different conclusion from three senior judges in England and Wales."
"It is important to emphasise that we are not concerned with the wider political issues which form the context for this legal issue ... The determination of this legal issue will not determine when and how the United Kingdom leaves the European Union."