Universal constraints

    fun verifyUniversalConstraints(tx: LedgerTransaction){

        val allStates = tx.inputsOfType<AgreementState>() + tx.outputsOfType<AgreementState>()

        for (s in allStates) {
            requireThat {
                "The buyer and seller must be different Parties." using (s.buyer != s.seller)
                "The proposer must be either the buyer or the seller." using (listOf(s.buyer, s.seller).contains(s.proposer))
                "The consenter must be either the buyer or the seller." using (listOf(s.buyer, s.seller).contains(s.consenter))
                "The consenter and proposer must be different Parties." using (s.consenter != s.proposer)
            }
        }
    }