The definition of symbiosis has varied among scientists. Some believe symbiosis should only refer to persistent mutualisms, while others believe it should apply to any type of persistent biological interaction (i.e. mutualistic, commensalistic, or parasitic).
The Golden Pledge, which is a System Plus Warranty with a 20 year leak guarantee, can pay for itself within the first ten years, sometimes many times over. The System Plus transforms the normal warranty by removing the small print.
A warranty is a contractual assurance made by a seller to a buyer and may be implicit or explicit. For example an explicit warranty for a watch may specifically say that it will last for at least 10 years. Implicit in this is that the watch is able to tell the time accurately.