Definition: f: X-->Y

f said to be loss at X to Y
if there is a and b on X s.t. f(a) = f(b)

모티베이션: 1+1 =2인데 2를보고 1+1인지 0+2인지 -100 +102인지 모르니까 이걸 정의화함

Theorem1: if f : X-->Y and g : Y-->Z is  loss each domain, the composite, g•f : X --> Z is loss at X to Z

Collary:

대충: f + g, f - g 이런것도 정보손실을 야기하는 함

이렇게 써내려가다 새로운걸 정의함

Definiton: S = {y : there is a and b in X s.t f(a)=f(b)}

is said to be Loss set of f

if S is open in Y, S is said to be open loss

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