Note that the declaration of parameters and return type for this inline closure is identical
to the declaration from the backwards function. In both cases, it is written as (s1: String, s2:
String) -> Bool. However, for the inline closure expression, the parameters and return type
are written inside the curly braces, not outside of them.
The start of the closure’s body is introduced by the in keyword. This keyword indicates
that the definition of the closure’s parameters and return type has finished, and the body
of the closure is about to begin.
Because the body of the closure is so short, it can even be written on a single line: