public static IGeometryAttributes DeleteFaces(this IGeometryAttributes g, Func <int, bool> predicate)
 => g.CopyFaces(i => !predicate(i));
 public static IGeometryAttributes CopyFaces(this IGeometryAttributes g, int from, int count)
 => g.CopyFaces(i => i >= from && i < from + count);
 public static IGeometryAttributes CopyFaces(this IGeometryAttributes g, IArray <bool> keep)
 => g.CopyFaces(i => keep[i]);