Task: Set
Go: package main

import "fmt"








type set map[complex128]bool

func main() {
    
    s0 := make(set)             
    s1 := set{3: true}          
    s2 := set{3: true, 1: true} 

    
    s3 := newSet(3, 1, 4, 1, 5, 9)

    
    fmt.Println("s0:", s0)
    fmt.Println("s1:", s1)
    fmt.Println("s2:", s2)
    fmt.Println("s3:", s3)

    
    fmt.Printf("%v ∈ s0: %t\n", 3, s0.hasElement(3))
    fmt.Printf("%v ∈ s3: %t\n", 3, s3.hasElement(3))
    fmt.Printf("%v ∈ s3: %t\n", 2, s3.hasElement(2))

    
    b := set{4: true, 2: true}
    fmt.Printf("s3 ∪ %v: %v\n", b, union(s3, b))

    
    fmt.Printf("s3 ∩ %v: %v\n", b, intersection(s3, b))

    
    fmt.Printf("s3 \\ %v: %v\n", b, difference(s3, b))

    
    fmt.Printf("%v ⊆ s3: %t\n", b, subset(b, s3))
    fmt.Printf("%v ⊆ s3: %t\n", s2, subset(s2, s3))
    fmt.Printf("%v ⊆ s3: %t\n", s0, subset(s0, s3))

    
    s2Same := set{1: true, 3: true}
    fmt.Printf("%v = s2: %t\n", s2Same, equal(s2Same, s2))

    
    fmt.Printf("%v ⊂ s2: %t\n", s2Same, properSubset(s2Same, s2))
    fmt.Printf("%v ⊂ s3: %t\n", s2Same, properSubset(s2Same, s3))

    
    delete(s3, 3)
    fmt.Println("s3, 3 deleted:", s3)
}

func newSet(ms ...complex128) set {
    s := make(set)
    for _, m := range ms {
        s[m] = true
    }
    return s
}

func (s set) String() string {
    if len(s) == 0 {
        return "∅"
    }
    r := "{"
    for e := range s {
        r = fmt.Sprintf("%s%v, ", r, e)
    }
    return r[:len(r)-2] + "}"
}

func (s set) hasElement(m complex128) bool {
    return s[m]
}

func union(a, b set) set {
    s := make(set)
    for e := range a {
        s[e] = true
    }
    for e := range b {
        s[e] = true
    }
    return s
}

func intersection(a, b set) set {
    s := make(set)
    for e := range a {
        if b[e] {
            s[e] = true
        }
    }
    return s
}

func difference(a, b set) set {
    s := make(set)
    for e := range a {
        if !b[e] {
            s[e] = true
        }
    }
    return s
}

func subset(a, b set) bool {
    for e := range a {
        if !b[e] {
            return false
        }
    }
    return true
}

func equal(a, b set) bool {
    return len(a) == len(b) && subset(a, b)
}

func properSubset(a, b set) bool {
    return len(a) < len(b) && subset(a, b)
}

Java: import java.util.Arrays;
import java.util.Collections;
import java.util.Set;
import java.util.TreeSet;

public class Sets {
    public static void main(String[] args){
        Set<Integer> a = new TreeSet<>();
        
        
        
        
        
        Set<Integer> b = new TreeSet<>();
        Set<Integer> c = new TreeSet<>();
        Set<Integer> d = new TreeSet<>();
        
        a.addAll(Arrays.asList(1, 2, 3, 4, 5));
        b.addAll(Arrays.asList(2, 3, 4, 5, 6, 8));
        c.addAll(Arrays.asList(2, 3, 4));
        d.addAll(Arrays.asList(2, 3, 4));
        System.out.println("a: " + a);
        System.out.println("b: " + b);
        System.out.println("c: " + c);
        System.out.println("d: " + d);
        
        System.out.println("2 in a: " + a.contains(2));
        System.out.println("6 in a: " + a.contains(6));
        
        Set<Integer> ab = new TreeSet<>();
        ab.addAll(a);
        ab.addAll(b);
        System.out.println("a union b: " + ab);
        
        Set<Integer> a_b = new TreeSet<>();
        a_b.addAll(a);
        a_b.removeAll(b);
        System.out.println("a - b: " + a_b);
        
        System.out.println("c subset of a: " + a.containsAll(c));
        
        
        System.out.println("c = d: " + c.equals(d));
        System.out.println("d = c: " + d.equals(c));
        
        Set<Integer> aib = new TreeSet<>();
        aib.addAll(a);
        aib.retainAll(b);
        System.out.println("a intersect b: " + aib);
        
        System.out.println("add 7 to a: " + a.add(7));
        System.out.println("add 2 to a again: " + a.add(2));
        
        
        Set<Integer> empty = Collections.EMPTY_SET; 
        
        empty.isEmpty(); 
        empty.size();
        Collections.disjoint(a, b); 
        Collections.unmodifiableSet(a); 
    }
}