Peano's axioms for Natural numbers.
3rd axiom from Introduction to topology by Bert Mendelson -
There is one and only one object in $\mathbb{N}$ denoted by $1$, which is not the successor of an object in $\mathbb{N}$, i.e, $1 \neq s(x)$ for each $x \in \mathbb{N}$.
How can $1$ not be a successor, isn't $0$ a natural number? Or Please explain what this statement says.
Note: I am not a maths student. Just reading that book out of curiosity.