Mark Krasnosel'skii died on February 13, 1997 at the age of 76.
Krasnoselskii fixed point theorem states that under certain sircumstances the operator has at least one fixed point in a subset of a Banach space. It doesn't say anything about uniqueness of solutions, just existence, but sometimes this is usefull enough, and perhaps you can get uniqueness by some other way. I hope this answers your question
Mark Spits is alive!
Mark Turbyfill died in 1991.
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