  We show that the problem of describing the conformations of a semiflexible
polymer confined to a channel can be mapped onto an exactly solvable model in
the so-called extended de Gennes regime. This regime (where the polymer is
neither weakly nor strongly confined) has recently been studied intensively
experimentally and by means of computer simulations. The exact solution
predicts precisely how the conformational fluctuations depend upon the channel
width and upon the microscopic parameters characterising the physical
properties of the polymer.
