====== UNION:  Union of Sets ======

**Explanation:** The function UNION is used either to combine two different sets of the same type into a resulting set:\\ e.g. //"The teacher asked all modelers and all handicraft enthusiasts of the school to prepare a contribution for the anniversary"//;\\ 
or to add a single element having type n to an already existing set of type (n+1):\\ e.g. //"All teachers and a student prepared the excursion."//\\ 
The latter case is needed for the representation of prepositions like //"including",// of connectors like //"and"// or of adverbs like //"additionally/in addition."//