No. but the story was inspired by the non-profit search-and-rescue group Liza Alert and the director, writer, Andrey Zvyagintsev's desire to make a film about a family.
The FAQ items below may give away important plot points.
Yes, he could be, even if his mother denied it, invoking that Alyosha had a birthmark. On the contrary, when Zhenya and Boris where providing information to the volunteers before the search, they recorded that Alyosha had no particular marks.
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