Functional analysis Mathematics 26 Functions of real variables 13 Measure theory 13 Operator theory 9 Differential equations, Partial 7 Congresses 6 Topology 6 Functions of complex variables 5 Mathematical optimization 5 Approximation theory 4 Banach spaces 4 Functions 4 Algebra 3 Control theory 3 Functional Analysis 3 Functional analysis -- Instructional exposition (textbooks, tutorial papers, etc.) 3 Integral representations 3 Linear topological spaces 3 Mathematical analysis 3 Metric spaces 3 Algebra, Boolean 2 Approximations and expansions 2 Functions of a Complex Variable 2 Functions of a complex variable 2 Geometry 2 Harmonic analysis 2 Harmonic analysis on Euclidean spaces 2 Hilbert algebras 2 Integration, Functional 2