Zhang Zhong-Jing, the source of the 1800 year old text, Treatise on Cold-Damage (Shang Han Lun) laid out six levels that an invading pathogen could be at a given time. Which of those is considered "the exterior" by us?
a. Tai Yang/Greater Yang
b. Yang Ming/Yang Brightness
c. Shao Yin (Lesser Yin)