static MacroCell construct(MacroCell hg, MacroCell hd,MacroCell bg, MacroCell bd){
		MacroCell m = new MacroCell(hg,hd,bg,bd);
		int n = m.hashCode();
		if(cellules.containsKey(n)) {return cellules.get(n);}
		else{cellules.put(n, m);return m;}
	}