[1] S. P. Avann: 
Metric ternary distributive semi-lattices. Proc. Amer. Math. Soc. 12 (1961), 407-414. 
MR 0125807 | 
Zbl 0099.02201[2] I. Chajda J. Niederle, B. Zelinka: 
On existence conditions for compatible tolerance relations. Czech. Math. J. 26 (1976), 304-311. 
MR 0401561[3] I. Chajda, B. Zelinka: 
Tolerance relation on lattices. Časopis pěst. mat. 99 (1974), 394-399. 
MR 0360380 | 
Zbl 0297.06001[4] L. Nebesky: 
Algebraic properties of trees. Acta Univ. Carol. Philologica-Monographia XXV, Praha 1969. 
MR 0274210 | 
Zbl 0214.23301[6] J. Nieminen: 
The congruence lattice of simple ternary algebras. manuscript, submitted to Časopis pěst. mat. 
Zbl 0504.08002[7] B. Zelinka: 
Tolerances and congruences on tree algebras. Czech. Math. J. 25 (1975), 634-647. 
MR 0387099 | 
Zbl 0327.08002[10] B. Zelinka: 
Tolerance relations on semilattices. Comment. Math. Univ. Carolinae 16 (1975), 333-338. 
MR 0369199 | 
Zbl 0326.06004