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function: restore_ripflags <1> -- undo cut
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keyboard equivalent: cmd/alt-z (w/focus on tools window!)

The "UNDO" button (lower right) swaps old and
current cuts (ripflags).  This toggles back and
forth between last two states of surface cuts.

Thus, this is a one-step-only undo/redo.

"UNDO" also unmarks all vertices.

To just unmark all vertices, do a R-click in the
surface display window.

See "INIT" and "ALL" for restoring initial cuts
or undoing all cuts.

N.B.: when mouse focus is on OpenGL window with
brain surface, the undo shortcut, cmd/alt-z,
instead restores a previously (e.g.,
accidentally) cleared set of vertex selections.

