. Okada I, Sasaki T, Nakai Y (2018) A solution for private assessment in indirect reciprocity using solitary observation. / Thew Blot 455:7-15. 38. Martinez-Vaquero IA Cuesta M (2013) Evolutionary stability and resistance to cheating in an indirect reciprocity model based on reputation. Phys Rev E 87: 052810. 39. Traulsen