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 Serrurier died in 1988.
Mark McPhee died in 1999.
Mark McCormack died in 2003.
Mark MacPhail died in 1989.
Mark Bytheway died in 2010.
Mark Sergeev died in 1997.
Mark Taper died in 1994.
Mark Sugden died in 1990.
Mark Clifton died in 1963.
Mark Fiennes died in 2004.