function showorhide(table)  {

        table.style.display = (table.style.display == "block" ) ? "none" : "block";

        if (table.id == "a" && table.style.display == "block")  {
       		b.style.display = "none";
        	c.style.display = "none";        	       
		}

        if (table.id == "b" && table.style.display == "block")  {
       		a.style.display = "none";
        	c.style.display = "none";       
		}

        if (table.id == "c" && table.style.display == "block")  {
			a.style.display = "none";
			b.style.display = "none";		       
		}
 
}; // end function