adds an element to a set
set2 = add_to_set(e,set1)
character string
set
set
The function add_to_set
creates a new set
set2
which is the set set1
to which is added the element
e
(a character string).
Note that if the element e
belongs already to the set set1
,
the set obtained
set2
is the same as the set
set1
.