FBoundedSimplification.scala

// does this work out?

trait Txn[S <: Sys] {
   def newVar[A](init: A): S#Vr[A]
}

trait Var[Tx, A] {
   def get(implicit tx: Tx): A
   def set(value: A)(implicit tx: Tx): Unit
}

trait Sys {
  type S = this.type // ! yes ??
  type Tx <: Txn[S]
  type Vr[A] <: Var[S#Tx, A]
}