South Korea: Criminal trials begins for impeached Yoon / Yoon Suk-yeol's 'invalid' impeachment sparks protests, political turmoil in South Korea / Thousands hit the streets for South Korea's impeached ex-president Yoon / Downtown Seoul tense as court rules on President Yoon's impeachment / South Korea constitutional court to rule on Yoon impeachment / South Korea's Constitutional Court to rule on Yoon's impeachment on Friday / South Korean court to rule on Yoon impeachment on April 4 / Rival rallies erupt in South Korea over President Yoon's impeachment / South Korea PM's impeachment rejected by court, Yonhap reports