Hi, There exists a very elegant algorithm to detect cycles in linked lists. https://en.wikipedia.org/wiki/Cycle_detection#Tortoise_and_hare I know that our LinkedList was written with the assumption that there are no cycles. However, it seems to me that it would be nice to have a test to check for cycles. This could be useful while printing or inspecting a LinkedList (and prevent things from blowing up when there is a cycle). Here is the implementation: LinkedList>>#containsCycle | slow fast | slow := fast := firstLink. [ slow notNil and: [ fast notNil and: [ fast nextLink notNil ] ] ] whileTrue: [ slow := slow nextLink. fast := fast nextLink nextLink. slow == fast ifTrue: [ ^ true ] ]. ^ false And one of the tests: LinkedListTests>>#testCycles 1 to: 42 do: [ :each | list := LinkedList withAll: (1 to: each). "Warning: the following statement creates a cylce, inspecting/viewing list will probably fail" list lastLink nextLink: list firstLink. self assert: list containsCycle ] Opinions ? Sven