How to show that the ordinary quiver of a semisimple algebra is a quiver consisting of isolated points? It is said that the ordinary quiver of a semisimple algebra is a quiver consisting of isolated points? How to prove this result? Thank you very much. Edit: the ordinary quiver is the quiver defined on page 59 of the book.

According to that definition, the arrows between points correspond to elements in the basis of $e_a(rad(A)/rad(A)^2)e_b$. In a semisimple ring, $rad(A)=\\{0\\}$, so such a basis would be empty.

So there are no arrows between distinct points.