A 
-subset is a subset
of a set on 
elements containing exactly 
elements. The number of 
-subsets
on 
elements is therefore given by the binomial coefficient 
. For example, there are 
2-subsets of 
, namely 
, 
,
and 
.
The 
-subsets of a list can be enumerated in
the Wolfram Language as Subsets[list,
k
].
The total number of distinct 
-subsets
on a set of 
elements (i.e., the number of subsets) is given by
 |
-Subsets." §1.5.5 in