49K05 Free problems in one independent variable
49K10 Free problems in two or more independent variables
49K15 Problems involving ordinary differential equations
49K20 Problems involving partial differential equations
49K22 Problems involving integral equations
49K24 Problems involving differential inclusions [See also 34A60]
49K25 Problems involving equations with retarded arguments [See also 34K35]
49K27 Problems in abstract spaces [See also 90C48, 93C25]
49K30 Optimal solutions belonging to restricted classes
49K35 Minimax problems
49K40 Sensitivity, stability, well-posedness [See also 90C31]
49K45 Problems involving randomness [See also 93E20]
49K99 None of the above, but in this section