K_4 Crystal (image) American Mathematical Society Caption K_4 crystal. Created by Hisashi Naito. Credit Hisashi Naito Usage Restrictions Obtain permission from Professor Toshikazu Sunada, email@example.com Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.