A new version of Collections was added to project The Inbox:
http://source.squeak.org/inbox/Collections-dtl.931.mcz

==================== Summary ====================

Name: Collections-dtl.931
Author: dtl
Time: 11 March 2021, 5:44:43.577146 pm
UUID: 1ed239e3-d108-43c3-8b6e-de8c43d842d1
Ancestors: Collections-nice.930

Set logic methods should be discoverable, so give them a method category. Add an implementation of Collection>>symmetricDifference: so that the basic set operations of union, intersection, difference, and symmetric difference are available.

=============== Diff against Collections-nice.930 ===============

Item was changed:
+ ----- Method: Collection>>difference: (in category 'set logic') -----
- ----- Method: Collection>>difference: (in category 'enumerating') -----
  difference: aCollection
  	"Answer the set theoretic difference of two collections."
  
  	^ self reject: [:each | aCollection includes: each]!

Item was changed:
+ ----- Method: Collection>>intersection: (in category 'set logic') -----
- ----- Method: Collection>>intersection: (in category 'enumerating') -----
  intersection: aCollection
  	"Answer the set theoretic intersection of two collections."
  
  	^ self select: [:each | aCollection includes: each]!

Item was added:
+ ----- Method: Collection>>symmetricDifference: (in category 'set logic') -----
+ symmetricDifference: aCollection
+ 	"Answer the set theoretic symmetric difference of two collections."
+ 
+ 	^ (self difference: aCollection) union: (aCollection difference: self)
+ !

Item was changed:
+ ----- Method: Collection>>union: (in category 'set logic') -----
- ----- Method: Collection>>union: (in category 'enumerating') -----
  union: aCollection
  	"Answer the set theoretic union of two collections."
  
  	^ self asSet addAll: aCollection; yourself!

Item was changed:
+ ----- Method: HashedCollection>>union: (in category 'set logic') -----
- ----- Method: HashedCollection>>union: (in category 'enumerating') -----
  union: aCollection
  	"Answer the set theoretic union of the receiver and aCollection, using the receiver's notion of equality and not side effecting the receiver at all."
  
  	^ self copy addAll: aCollection; yourself
  
  !