chickadee » srfi-113 » set-difference!

set-union! set1 set2 ...procedure
set-intersection! set1 set2 ...procedure
set-difference! set1 set2 ...procedure
set-xor! set1 set2procedure

Linear update procedures returning a set that is the union, intersection, asymmetric difference, or symmetric difference of the sets. Asymmetric difference is extended to more than two sets by taking the difference between the first set and the union of the others. Symmetric difference is not extended beyond two sets. Elements in the result set are drawn from the first set in which they appear.