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R := {[x]:x > 1 }; R; R2 := subsetof R; R2; R - R2; R subset R2; R2 - R; R2 subset R; S := {[x]: x > 0}; S - R; R subset S; S - R2; R2 subset S; S2 := {[x]: x > -1}; S3 := subsetof S2; S3 - S; S subset S3;