What Zoro used in Alabasta was Emission Armament. The way he used it there was exactly as Hyogoro explained how to do Emission Haki. These things are simple logical deduction based on the evidence provided within the manga. It is an advanced form of Armament on a lower level than Internal Armament is.
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And no. This is not how you defeat a Gorosensei. Just to add salt to the wound, I hope Kizalu meets his end by the hands of the Gorosenseis.