The difference between 2 collections: collection2 subtracted from collection1.

Example: for A,B,C,D and B,C,D,E,F the difference is A.

Set{'a','b','c','d'}->difference(Set{'b','c','d','e'})
= 'a'

Set{'a','b','c','d','e'}->difference(Set{'b','c','d','e'})
= 'a'

Set{'a','b','c','d','e','f'}->difference(Set{'b','c','d','e'})
='a','f'

Set{'a','b','c','d','e','f'}->difference(Set{'a','b','c','d','e','f'})
= empty

Set{'a','b','c','d','e','f'}->difference(Set{'a','b','c','d','e','f','g'})
= empty

Set{'a','b','c','d','e','f','g'}->difference(Set{'a','b','c','d','e','f'})
= 'g'

See: Examples_on_collection_operators

In Linq, this can be achieved with "Except".

See also: OCLOperators_symmetricDifference

Video: OCL Operators: difference