Pair constructor Pair(x, y) was used in thread and traversals for distribution of environments during traversal.
The Pair constructor has become obsolete with the introduction of FixedLengthTuple in StrategoRelease07.
Until StrategoRelease071 the Pair constructor will be defined as an overlay
overlays Pair(x, y) = (x, y)-- EelcoVisser - 06 Jan 2002