...medium.

We use the term crest line, not front line, to avoid confusion with the close, but distinct `eikonal-curvature' approach or Fife limit [12, 13, 14], which describes the broken excitation wave by two curves, its front and back, with their junction being the wave tip.

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...form

Here we include higher-order terms with coefficients 78#78 which can be obtained in the next order of the same perturbation technique

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