Modal logic 1.5a - soundness & completeness

[@maxysexy69]

video starts at 1:26. Welcome :-)

[@kennedyandjory]

This was great - made the concepts super clear.

[@user-gm3lg8gp3m]

This was really helpful, Thanks a lot!

[@nammzzi9424]

thanks made things clearer.
fyi, great voice XD

[@ffhashimi]

very important !

[@movax20h]

This appears it have nothing to do directly with modal logic. It is more general notion in logic.
Also, the video doesn't answer important question, is system k with trees, sound or complete.