EqSourceEq plugin: receive another value as inherited attribute and test for equality.
Very similar to Compare plugin.
For type declaration type ('a,'b,...) typ = ... it will create a transformation function with type
('a -> 'a -> bool) -> ('b -> 'b -> bool) -> ... -> ('a,'b,...) typ -> bool
Inherited attribute' is the same as argument, synthetized attribute is GT.comparison.