Editing Denotational semantics (section)

===Denotational semantics of sequentiality===
The problem of full [[Denotational semantics#Abstraction|abstraction]] for the sequential programming language [[Programming language for Computable Functions|PCF]] was, for a long time, a big open question in denotational semantics. The difficulty with PCF is that it is a very sequential language. For example, there is no way to define the [[logical disjunction#parallel-or|parallel-or]] function in PCF. It is for this reason that the approach using domains, as introduced above, yields a denotational semantics that is not fully abstract.

This open question was mostly resolved in the 1990s with the development of [[game semantics]] and also with techniques involving [[logical relations]].<ref>{{cite journal |first1=P.W. |last1=O'Hearn |first2=J.G. |last2=Riecke |title=Kripke Logical Relations and PCF |journal=Information and Computation |volume=120 |issue=1 |pages=107–116 |date=July 1995 |doi=10.1006/inco.1995.1103 |s2cid=6886529 |url=https://surface.syr.edu/lcsmith_other/3 |doi-access=free }}</ref> For more details, see the page on PCF.