No failure or delay on the part of the Company or Purchaser to exercise any right, power or remedy shall operate as a waiver thereof, nor shall any single or partial exercise of any such right, power or remedy preclude any other or further exercise thereof or the exercise of any other right, power or remedy under this Agreement. No amendment, modification or waiver of any provision of this Agreement shall be effective unless the same shall be in writing signed by the Company and Purchaser.