First, when i studied group action, i found out about design theory, then i got interested in it. But is there any good book to study design theory? especially for introduction and undergraduate student level. I knew about Design Theory book athor by Thomas Beth, D. Jungnickel, H. Lenz. But i find it too way long and i thought it is not introduction level. Pleas inform me if you know anything about it, thank You so Much!