- #1
Figaro
- 103
- 7
Homework Statement
Let ##X## and ## Y## be non-empty sets, ##i## be the identity mapping, and ##f## a mapping of ##X## into ##Y##. Show the following
a) ##f## is one-to-one ##~\Leftrightarrow~## there exists a mapping ##g## of ##Y## into ##X## such that ##gf=i_X##
b) ##f## is onto ##~\Leftrightarrow~## there exists a mapping ##h## of ##Y## into ##X## such that ##fh=i_Y##
Homework Equations
The Attempt at a Solution
a) ##~\Rightarrow~## Since ##f## is one-to-one, there exist ##y \in Y## such that ##y=f(x)## for some ##x\in X##, this shows that there exist at least some mapping ##g## that maps ##Y## into ##X## such that ##x=g(y)=g(f(x))=(gf)(x)## for some ##y##, and also ##gf=i_X##.
b) ##~\Rightarrow~## Since ##f## is onto, for all ##y\in Y## there exist some ##x\in X## such that ##y=f(x)##, this shows that there exist some mapping ##h## of ##Y## into ##X## such that ##x=h(y)## and ##y=f(x)=f(h(y))=(fh)(y)## which implies ##fh=i_Y##.
I have done the forward proof but I just want to know if my proof here is correct.