English to Russian Law/Patents Law: Contract(s)

Amendments and Waivers.

This Agreement may not be amended except by an instrument in writing signed on behalf of each of the parties hereto.

By an instrument in writing, Purchaser, on the one hand, or Seller, on the other hand, may waive
compliance by the other with any term or provision of this Agreement that the other party was or
is obligated to comply with or perform. Such waiver or failure to insist on strict compliance with
such term or provision shall not operate as a waiver of, or estoppel with respect to, any
subsequent or other failure of compliance.

...

Про estoppel читал, но как его облечь в читаемую форму в данном контексте?

не является отказом от права требовать выполнения [такого условия или положения] или ...?