kniha1=new Image();
kniha1.src="obr/kniha_m.jpg";
kniha2=new Image();
kniha2.src="obr/kniha_m2.jpg";

ex1=new Image();
ex1.src="obr/ex1.jpg";
ex2=new Image();
ex2.src="obr/ex2.jpg";

word1=new Image();
word1.src="obr/word1.jpg";
word2=new Image();
word2.src="obr/word2.jpg";

acc1=new Image();
acc1.src="obr/acc1.jpg";
acc2=new Image();
acc2.src="obr/acc2.jpg";

function zamen(prvy,druhy)
	 {
	 document.images[prvy].src=druhy.src;
	 }