There is a way to do this, but it involves quite a bit of work. I had thought I had found a quick solution, "Flip Across" in the Brush Options dialog box, but it does not work. It's just another way of "Reversing the Path." What you need to create is the exact same Brush flipped along a vertical axis. To do this, try the following: Click and drag your existing Rope Brush out of the Brushes panel to alter the original vector. (Don't worry, the original Brush will remain in the Brushes panel untouched). You will probably see several square Pattern tiles. (Depending on the Pattern Brush, there could be up to five squares. The first is the way Outside Corners are treated, the second is for the running Sides, then Inside Corners, the Start and the End of the Brush. The Tiles will be Grouped together. With the Tiles selected, double-click on the Reflect tool (0) and flip the Tiles across a Vertical Axis. Go to Object Ungroup, to Ungroup the Tiles. Now you need to make each Tile into a Pattern, so it can be part of your Flipped Rope Brush Select each Tile, one at a time, and go to Window > Pattern Options to open the Patten Options panel. Go under the Options menu of the panel and select Make Pattern and press OK. Then press Done (under the Control panel) to escape Pattern Editing mode and add the Pattern to the Swatches panel. Repeat for each Tile in the Brush. To create a Reflected version of your Rope Brush, do the following: Select the Reflected Side Tile, which would be the main part of your Rope Brush, and drag it into the Brushes panel to create a new Brush. Make sure to select Pattern Brush in the New Brush window that opens and click OK. In the dialog that opens, add your newly created Patterns to the appropriate part of the Brush (Outside Corners, the running Sides which should already be there, Inside Corners, Start and End). Click OK to created your Reverse Rope Brush. Then Copy your original Rope path, and paste in front. Apply your new Reverse Rope Brush and go to Object > Path > Reverse Path Direction. This will reverse the stacking order of the anchor points in the path as if it were drawn in the opposite direction. Then create a Mask for the overlap area only. This should work! Please let me know how you make out with it. See example below!
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