Forum:Silent Swordsman Cards

So me and my friend had a pretty heated argument about a new deck I put together.

I have a silent swordsman deck, and he is arguing 2 points about my Silent Sword Slash card.

1. He thinks that the atk/def boost from silent sword slash is not permanent. 2. He thinks that Silent Sword Slash can not be used on Silent Swordsman Lvl 7, because of silent swordsmans effect, and cause of card chain.

I know from playing with them in the past that the atk/defense boost is permanent, and that it is the immunity to card effects that end after 1 turn. I also know that you can use Silent Sword Slash on Silent Swordaman lvl 7, because it says its activation and effect cant be negated. Am i correct, or did i read it wrong. I know this is how it works in the Duel Links game too.