The uses of "Yi" in "Li-Sau" comprise of the four categories: preposition, connective, adverb, and verb.
1.PREPOSITON
When "Yi" is used as a preposition, it combines with a predicate to form the preposition-predicate structure after a verb. This structure would be either a complement or an adverbial modifier.
2.CONNECTIVE
"Yi" as a connective can associate the antecedent with the consequent to mean: (1)a juxtaposition; (2)a continuation; (3)an extension; (4)a goal; (5)a reason; (6)a modification; and (7)a transition.
3.ADVERB
"Yi" as an adverb can quality a trailing verb or adjective.
4.VERB
"Yi" as a verb represents a subconsious action such as judgment or confirmation.
Statistically, there are 77 sentences consist of the word "Yi" in a total of 373 sentences from "Li-Sau". The importance of "Yi" in "Li-Sau" is obviously vindicated from this 20%+ percentage.