(* booleanExpression.ml *)
type 'canonical generic_boolean_expression = [
  `Variable of int |
  `Not of 'canonical generic_boolean_expression |
  `And of 'canonical generic_boolean_expression list |
  `Or of 'canonical generic_boolean_expression list
];;

type boolean_expression = [`Not_Canonical] generic_boolean_expression;;

(* booleanExpression.mli that works *)
type boolean_expression = [
  `Variable of int |
  `Not of boolean_expression |
  `And of boolean_expression list |
  `Or of boolean_expression list
];;

(* booleanExpression.mli that doesn't work and I don't understand why... *)
type boolean_expression;;