 Another, completely different approach to full abstraction, exploits special kinds of logical relations in order to isolate quotients of the continuous model. The first use of logical relations in the context of the problem of full abstraction is Mulmuley 1987, but the resulting construction of a fully abstract model is obtained by brute force and therefore is not what the full abstraction problem searches for. Later, Sieber (1992) and O’Hearn &amp; Riecke (1995) have employed refinements of this technique to gain a better insight into the structure of the fully abstract models, characterizing the definable elements of the standard continuous model by means of invariance under special logical relations cutting out the non-sequential functions.