Question: Were Mark Krein and Lev Pontryagin from the same country?
Sentence (from "Lev Pontryagin"): Despite his blindness he was able to become one of the greatest mathematicians of the 20th century, partially with the help of his mother Tatyana Andreevna who read mathematical books and papers (notably those of Heinz Hopf, J. H. C. Whitehead, and Hassler Whitney) to him.
Relevant evidence: No