  Liquid crystalline systems exhibiting both macroscopic chirality and smectic
order experience frustration resulting in mesophases possessing complex
three-dimensional order. In the twist-grain-boundary phase, defect lattices
mediate the propagation of twist throughout the system. We propose a new chiral
smectic structure composed of a lattice of chiral bundles as a model of the
helical nanofilament (B4) phase of bent core smectics.
