Full Idea
A classic reduction is the class of ordered pairs <x,y> being reduced to the class of sets of the form {{x},{x,y}}.
Gist of Idea
The ordered pairs <x,y> can be reduced to the class of sets of the form {{x},{x,y}}
Source
Michael Dummett (Frege Philosophy of Language (2nd ed) [1973], Ch.14)
Book Reference
Dummett,Michael: 'Frege Philosophy of Language' [Duckworth 1981], p.477