overlappingPairs in Smalltalk

coll := #(1 2 3 4 5 6).

overlappingPairs := (coll overlappingPairsCollect: [ :a :b  | {a. b} ]).

overlappingPairs2 := OrderedCollection empty.
(Polygon vertices: coll) segmentsDo: [ :a :b |
    overlappingPairs2 add: { a. b }
].
overlappingPairs2 removeLast.

overlappingPairs2 >>> overlappingPairs.