In the commentary of "11.1.1 Direct sum of left modules" the definition of wikipedia and that of Lang amount to the same. We can settle for Lang's.
Let's favor the book. It looks better. -- FL -- You received this message because you are subscribed to the Google Groups "Metamath" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/metamath/46fadbdb-71a6-496d-b91c-cec4f194dc0f%40googlegroups.com.
