Richard wrote

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I would check this in Pharo, but have so far failed to get it running under Ubuntu 17.10. Squeak _is_ running there, sort of, and the definition of #permutationsDo: in Interval is this code: permutationsDo: aBlock "Repeatly value aBlock with a single copy of the receiver. Reorder the copy so that aBlock is presented all (self size factorial) possible permutations." "(1 to: 4) permutationsDo: [:each | Transcript cr; show: each printString]" self asArray permutationsDo: aBlock Exactly the same comment is found in SequenceableCollections. Are you sure that Pharo has something different? "with a SINGLE COPY of the receiver" is pretty important. ... <<< Thanks Richard. The Pharo comment is identical. The problem was simply that I hadn't understood what it was - quite clearly - telling me. Now that I understand the problem, the explanation makes perfect sense :-) Cheers Andy