South Korean investigators on Friday pressed ahead with their probe into impeached President Yoon Suk Yeol over his Dec. 3 martial law declaration, issuing another summons demanding that he appear for questioning on Christmas Day, despite his continued refusal to cooperate. The Corruption Investigation Office for High-Ranking Officials, which is leading a joint investigation with police and military authorities on Yoon’s ill-conceived power grab that lasted only several hours, said it plans to question Yoon on charges of orchestrating a rebellion and abuse of authority.