Answer:
negotiation.
Explanation:
Negotiation is the process addressed, through which both the parties in an agreement reach to a conclusion, which is favorable to both, as both parties tend to lose some benefit, or tend to incur some cost.
Through negotiation no third party is involved.
Already existing parties in an agreement compromise on certain things allowing, the agreement to validate and to proceed with the same agreement.
Therefore, correct option is:
negotiation