10. Escalation clauses are not void per se. 11. The determination of the performance may be left to a third person, whose decision shall not be binding until it has been made known to one of the contracting parties. 12. Laws in force at the time the contract was made generally govern its interpretation and application. 13. There must be mutuality between the parties based on their essential equality to which is repugnant to have one party bound by the contract leaving the other free therefrom. 14. A contract containing a condition which makes its fulfilment dependent exclusively upon the uncontrolled will of one of the contracting parties, is valid. 15. It is basic that there can be contract in the true sense in the absence of the element of agreement, or of mutual assent of the parties. 16. A contract of lease is generally transmissible to the heirs of the lessor or lessee. 17. Once the minds of the contacting parties meet, a valid contract exists, whether it is reduced to writing or not. 18. It is correct to conclude that contracts of adhesion are invalid per se. 19. A contract of adhesion becomes void only when the dominant party takes advantage of the weakness of the other party. 20. The freedom of contract is not absolute