Countable subadditivity of a set function 
is the property that, for any countable
collection of sets 
for which 
is defined both on each 
and on their union,
 |
A set function possessing countable subadditivity is said to be countably subadditive.
Any countably subadditive set function 
is also finitely subadditive
presuming that 
,
where 
is the empty set.
