  This survey paper reports on the properties of the fourth-order Bessel-type
linear ordinary differential equation, on the generated self-adjoint
differential operators in two associated Hilbert function spaces, and on the
generalisation of the classical Hankel integral transform. These results are
based upon the properties of the classical Bessel and Laguerre secondorder
differential equations, and on the fourth-order Laguerre-type differential
equation. From these differential equations and their solutions, limit
processes yield the fourth-order Bessel-type functions and the associated
differential equation.
