Külzer, Stephanie. “Formal and Informal Instruments: How Can They Best Complement Each Other? Exemplarily Illustrated through the Planning Determination Process and Regional Dialogue Forum for the Extension of Frankfurt Airport”. Raumforschung und Raumordnung | Spatial Research and Planning 67, no. 4 (July 31, 2009): 318–329. Accessed May 17, 2025. https://rur.oekom.de/index.php/rur/article/view/985.