public override void Cross(ref ChromosomeBase x)
		{
			// cut point and lenght
			int cut, cut_l;
			cut = Globals.rnd.Next( TPChromosome.chromosome_size );
			cut_l = Globals.rnd.Next( TPChromosome.chromosome_size - cut );
			
			// preparing for the cross
			TPChromosome xx = (TPChromosome)x;
			ArrayList sec1, sec2;
			sec1 = (ArrayList)this.genes.GetRange( cut, cut_l ).Clone();
			sec2 = (ArrayList)xx.genes.GetRange( cut, cut_l ).Clone();

			// crossing
			for ( int i=0; i < this.genes.Count; i++ )
				if ( sec2.Contains( this.genes[i] ) ) { this.genes.Remove( this.genes[i] ); i--; };
			this.genes.InsertRange( cut, sec2 );
			for ( int i=0; i < xx.genes.Count; i++ )
				if ( sec1.Contains( xx.genes[i] ) ) { xx.genes.Remove( xx.genes[i] ); i--; }
			xx.genes.InsertRange( cut, sec1 );

#if DEBUG
			System.Diagnostics.Trace.WriteLine( "\n" + cut.ToString() + " " + cut_l.ToString()  );
			System.Diagnostics.Trace.WriteLine( this.GetRepresentation() );
			System.Diagnostics.Trace.WriteLine( xx.GetRepresentation() );
#endif
		}