Original: It was joined by pro-Pierre Mendès-France clubs (Union of Clubs for the Renewal of the Left led by Alain Savary) and left-wing republican groups (Union of Socialist Groups and Clubs of Jean Poperen).
Simplified: It was joined by pro-Pierre Mendès-France clubs (Union of Clubs for the Renewal of the Left led by Alain Savary) and left-wing republican groups (Union of Socialist Groups ad Clubs of Jean Poperen).