var d=new Date();

var day=new Array(7);
day[0]="<link rel='stylesheet' type='text/css' href='style/a.css'>";
day[1]="<link rel='stylesheet' type='text/css' href='style/b.css'>";
day[2]="<link rel='stylesheet' type='text/css' href='style/c.css'>";
day[3]="<link rel='stylesheet' type='text/css' href='style/d.css'>";
day[4]="<link rel='stylesheet' type='text/css' href='style/e.css'>";
day[5]="<link rel='stylesheet' type='text/css' href='style/f.css'>";
day[6]="<link rel='stylesheet' type='text/css' href='style/g.css'>";

document.write(day[d.getDay()]);