Solutions To Mathematics Textbooks/Proofs and Fundamentals/Chapter 4
Exercise 4.1.1
[edit | edit source](1), (3) and (6) are functions.
Exercise 4.1.2
[edit | edit source]The first one and the fourth one are functions (here I've assumed that "mother" and "father" were meant biologically, and that not everyone has precisely one person they'd call a "best friend").
Exercise 4.1.3
[edit | edit source](i) and (iv) represent functions.
Exercise 4.1.4
[edit | edit source](2) and (3) properly describe functions.