Inverse problems in differential equations constitute a pivotal area in applied mathematics and engineering, where the aim is to deduce unknown parameters or inputs within a differential equation ...

Daniel Richardson, Some Undecidable Problems Involving Elementary Functions of a Real Variable, The Journal of Symbolic Logic, Vol. 33, No. 4 (Dec., 1968), pp. 514-520 ...

Since every plane-harmonic function is associated with a conjugate, problems in which normal gradients are specified on the boundary can be transformed into problems in which boundary values are ...