function solution() {
    class Hall {
        constructor(capacity, name) {
            this.capacity = capacity;
            this.name = name;
            this.events = [];
        }

        hallEvent(title) {
            if (!this.events.includes(title)) {
                this.events.push(title);
                return 'Event is added.'
            }else {
                throw new Error('This event is already added!');
            }

        }
        close(){
            this.events=[];
            return `${this.name} hall is closed`;
        }
        toString(){
            let output=[];
            output.push(`${this.name} hall - ${this.capacity}`);
            if(this.events.length>0){
                output.push(`Events: ${this.events.join(", ")}`);
            }
            return output.join('\n');
        }
    }
    class MovieTheater extends Hall{
        constructor(capacity,name,screenSize) {
            super(capacity,name);
            this.events=[];
            this.screenSize=screenSize;
        }
        close(){
            return `${super.close()}All screenings are over.`
        }
        toString() {
            return `${super.toString()}\n${this.name} is a movie theather with ${this.screenSize} screensize and ${this.capacity} seats capacity.`;

        }

    }
    class ConcertHall extends Hall{
        constructor(capacity,name){
            super(capacity,name);
            this.events=[];
            this.performers=[];
        }
        hallEvent(title,performers){


            if(this.events.includes(title)){
                throw new Error('This event is already added!');
            }
               this.events.push(title);
               this.performers.push(...performers);
               return `Event is added.`;
        }
        close(){
            this.performers=[];
            return `${super.close()} All performances are over.`
        }
        toString() {
            let output=[super.toString()];
            if(this.performers.length>0){
                output.push(`Performers: ${this.performers.join(', ')}.`);


            }
            return output.join('\n')

        }
    }


    return {
        Hall,
        MovieTheater,
        ConcertHall,
    }

}