I want to know the answer to the following question:
What did Yaroslav sons achieve  during his time in Keivan Rus?
All the background I'm provided with is that "Kievan Rus' reached its greatest extent under Yaroslav I (1019–1054); his sons assembled and issued its first written legal code, the Rus' Justice, shortly after his death.". Is that enough to answer the question?
Answer: yes