Defining Functions in Terms of Other Functions

We could define a function isEven:num -> boolean as follows:

 
isEven:num -> bool;
isEven(n) <=  if n mod 2 = 0
              then true
              else false;

or even more simply as

 
isEven:num -> bool;
isEven(n) <= n mod 2 = 0;

or we could use the previously defined isOdd function:

 
isEven:num -> bool;
isEven(n) <= not (isOdd(n));