Nigerian judges are hearing three cases aimed at clarifying who rules in the absence of President Umaru Yar’Adua, still in hospital in Saudi Arabia.
Judges are to decide whether government actions taken since Mr Yar’Adua left in November are legally binding.
Government critics say the president acted illegally when he failed to hand power formally to his vice-president.
But a court ruling on Wednesday backed the government, saying the constitution did not require such a transfer.
Mr Yar’Adua has been receiving treatment for a heart condition since late November.
His prolonged absence led to rumours that he was brain damaged or even dead.
It is not clear when the judges will deliver their rulings.
The BBC’s Caroline Duffield in Abuja says even senior cabinet ministers seemed to be mystified, openly admitting they did not know when he would return.
She says Nigerians are watching the court cases very closely after all the uncertainty and political anxiety of recent weeks.
Analysts said Wednesday’s ruling appeared to preserve the status quo – that Vice-President Goodluck Jonathan was in charge, but could not be regarded as official head of state.
But human rights lawyer and opposition activist Femi Falana, who is bringing one of Thursday’s cases, dismissed the ruling as “meaningless”.
“Jonathan cannot act for Yar’Adua because no functions have been formally and directly delegated to him by Yar’Adua,” the AFP news agency quoted him as saying.
Mr Falana is asking the court to annul all decisions taken by the cabinet during the president’s absence.
In another of Thursday’s cases, the Nigerian Bar Association is demanding that power is handed over formally to Mr Jonathan.
And in the third case, a rights group wants Mr Yar’Adua declared “missing”.
Mr Yar’Adua has not been seen in public since he was taken to hospital in November, but he gave an interview to the BBC on Tuesday saying he was recovering and hoped to be able to resume his duties.
Doctors say he is suffering from acute pericarditis – inflammation of the lining of the heart.
He also has a long-standing kidney complaint.
SOURCED FROM BBC