Sommaire

Contents
Cyclicity in a special class of hypergroups
p. 3-6
The set of hypergroups with operators which are constructed from a set with two elements
p. 7-10
Remarks on tolerance algebras
p. 11-16
On a class of subdirectly irreducible groupoids
p. 17-24
A note on subdirectly irreducible groupoids
p. 25-28
On a class of groupoids
p. 29-49
Motion of cometary particle with variable mass under central fields of forces
p. 51-61
Radiation transfer in circumstellar dust envelopes with spherical symmetry - Henyey's method of solution
p. 63-75