*Let*: in order to make building a more elaborate system easier, it is possible to define values using `let`.
In this toy system, `let`s should only be used at the beginning of a file. If we have, for intance,
*Let*: in order to make building a more elaborate system easier, it is possible to define values using `let`.
In this toy system, `let`s should only be used at the beginning of a file. If we have, for intance,