to be unstable to the L or C phases at high enough $\chi N$.[@Fors+94]

Although several groups attempted to describe this transition theoretically,[@MayeDela91; @JoneDela94; @HamlBate94] using variations on Leibler’s theory, the first successful theory is due to Matsen and Schick [@MatsSchi94e], who developed a method for computing the free energy of any crystalline structure by expanding the partition function in the basis functions for the symmetry of the desired mesophase, rather than the Fourier mode expansion of Leibler. They found a stable gyroid phase for $11.14 < \chi N \alt 60$, where the upper limit was determined by extrapolation from the phase boundaries at lower $\chi N$.[@MatsBate96] This was followed by careful application of Leibler’s method,[@milner97; @podneks96] to include higher harmonics and calculate the stability of the G phase in weak segregation analytically.

Roughly concurrent to the calculations of Matsen and Schick, methods were developed to calculate the free energy of essentially arbitrary structures in the strong segregation regime ($\chi N\rightarrow\infty$). [@olmsted94a; @LikhSeme94]. These methods use the results for polymer brushes,[@semenov85; @mwc88a], supplemented by an ansatz about the geometry of the relevant phase and an assumption about the chain paths. Olmsted and Milner assumed straight paths through the $A\!-\!B$ interface 