Use and to define multiple items in one mutually-recursive group.
and
let rec ... and ...
let rec isEven = n => n == 0 || isOdd(n - 1) and isOdd = n => n != 0 && isEven(n - 1)
type rec ... and ...
type rec expr = Add(expr, term) | Term(term) and term = Int(int)
Recursive Functions
Type