...group

We consider only the subgroup of orientation-preserving motions.

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...and arguments of w.

Equivalently, the semi-reduced system can be obtained by combining (2) and (3) and identifying with , so that (19) corresponds to (4). The group , is represented in the semi-reduced system (2)+(3) by shifts in .

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...exact relation to the PDE system (21).

In fact, computations with smaller steps give different behaviour (R. Mantel, private communication).

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