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Proper Subset:   A proper subset is a special type of subset.  There are two requirements for set A to be a proper subset of set B.  They are:

               1.  A is a subset of B, i.e., A B   and
               2.  A is not equal to B, i.e., A B.

Notation: A
B is read, “Set A is a proper subset of set B.

Example:  The set of members of the U.S. Senate’s Judiciary Committee is a subset of the set of members of the U.S. Senate since not every member of the U.S. Senate is on the Judiciary Committee.

Example:
  For A = {red, blue} and B = {red, white, blue}, A
B since both requirements are met:
                         1.   A
B since red and blue are in both sets A and B; and
             
           2.   A
B since set B contains the element “white” but set A does not.

 Listing Proper Subsets:   List all the proper subsets of {a, b, c}.                 
 

Example:  The set {a, b, c} has 7 proper subsets.  They are:  
                     
, {a}, {b}, {c}, {a, b}, {a, c}, and {b, c}.

 

Note that {a, b, c} is not a proper subset of {a, b, c}. Also, note that there is always one less proper subset than there are subsets of a set since a set cannot be a proper subset of itself.