This Quotable represents an important Quotable construction mechanism.
Provided some Quotable object plus the definition of some so called "equivalence relationship", then this Quotable here represents the set of all Quotable objects that are "equivalent" to the given object in accordance with the given "equivalence relationship".
A simple example of such a construction is the "Discount Quotable Curve", which can be derived from a specific Discount Quotable object (eg a USD matured in 10 Mar 2020") together with the "equivalence relationship" that stipulates that any two Discount Quotable objects with the same currency are deemed to be "equivalent".
The resulting "Discount Quotable Curve" can thus be seen to model the whole set of Discount Quotables wrt a given currency regardless of their maturity.
It is natural to identify this concept with a "Discount Quotable Curve" whose value at any time is a mathematival one-dimensional curve.