Astrologie een wetenschap, book, [1965..1973]; (https://texashistory.unt.edu/ark:/67531/metadc674/m1/1/: accessed June 20, 2024), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu; .
Astrologie een wetenschap, book, [1965..1973]; (https://texashistory.unt.edu/ark:/67531/metadc674/m1/1/: accessed June 20, 2024), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu; .