Complex sentence: To each according to his contribution has been mentioned in various forms by many members of the labor movement, from Ferdinand Lassalle's and Eugen Duhring's statements to Leon Trotsky.
Split into simpler sentences: To each according to his contribution was a concept espoused by many members of the labor movement. Examples would be found of this in Ferdinand Lassalle's and Eugen Duhring's statements to Leon Trotsky.