Mathematics

Problem

Which one of the following statements correctly defines a one–to–one (injective) function

f:A\to B

? a) Every vertical line meets the graph of

f

at most once b)

f(x_1)=f(x_2)

implies

x_1\neq x_2

f(x_1)=f(x_2)

implies

x_1=x_2

f(x_1)\neq f(x_2)

implies

x_1=x_2