speck PreconditionTest {

state: {
  balance: Integer
  active: Boolean
}

action SetBalance(newBalance: Integer) {
  precondition: newBalance >= 0
  postcondition: this.balance == newBalance
  require newBalance >= 0
  this.balance := newBalance
}

action Deactivate() {
  precondition: this.balance == 0
  or this.active == false
  postcondition: this.active == false
  this.active := false
}

}