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Call the image with the three of them side by side image 1, and the closeup of their intersection image 2.
Image 1 has pieces A, B, and C side by side.
Image 2 has piece C going from top left to bottom right, piece A going from bottom left to top right, and piece B going from center bottom to center top.
Focus first on piece C- in image 2, it’s just rotated slightly counterclockwise from its orientation in image 1 (and tilted forward). Next see how piece A is fit into piece C: in image 1, piece A in this configuration would be skinny-side forward, forming a cross with piece C. Now piece C only has one channel through which extra wood could fit, so observe how piece B threads nicely through that channel, while also making room for piece A to pass through. Beautiful.