Heldenfels, H. C. [Letter from H. C. Heldenfels to Harris L. Kempner, April 29, 1966], letter, April 29, 1966; (https://texashistory.unt.edu/ark:/67531/metapth1427842/m1/2/: accessed July 17, 2024), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu.; .