R. Yehoshua says: All who are liable to judicial death penalty — the child is a mamzer, it being written "A man shall not take the wife of his father … A mamzer may not come, etc." Just as "the wife of his father" is distinct in being subject to judicial death penalty and the child is a mamzer, so, in all who are thus characterized, the child is a mamzer.
"even the tenth generation": It is written here "the tenth generation," and below (4) (in respect to an Amoni and a Moavi) "the tenth generation." Just as "the tenth generation" there is for all time, so, "the tenth generation" here.