Ratio Mathematica – n. 13 / 1999

Sur la valuation striate des hypergroups polysymetriques canoniques 
J. Mittas, pag. 5
 

Ideals in a semihypergroup and Green’ s relation 
A. Hasankhani, pag. 29

Hypercompositional structures from the computer theory 
G. G. Massouros, pag. 37
 
Closure system and closure hypergroups,  
D. Lenzi, pag. 43
 
On some applications of fuzzy sets and commutative hypergroups to evaluation in architecture and town-planning, 
B. Ferri e A. Maturo, pag. 51
 
Homomorphic relations on hyperringoids and join hyperrings 
G. G. Massouros e C. G. Massouros, pag. 61
 
Lower and upper approximation in H – groups 
B. Davvaz, pag. 71