Letter of gratitude (2020) is based on an ink drawing by the American artist Brice Marden. Tillers has included another version of this image in the top left corner of Terra Nullius, 2020. He has been attracted to the work of Marden over the years because of its resonance with Australian artists such as Emily Kngwarreye and Ian Fairweather. The calligraphic lines also evoke the idea of an interconnected network, an idea that relates to Tillers’ ongoing project ‘The Book of Power’ or ‘The Canvasboard System’.