Points of Continuity, Quasicontinuity, Cliquishness, and Upper and Lower Quasicontinuity
Ján Borsík · Real Analysis Exchange · 2008
The quadruplet $(C(f), Q(f), E(f), A(f))$ is characterized, where $C(f)$, $Q(f)$, $E(f)$ and $A(f)$ are the sets of all continuity, quasicontinuity, upper and lower quasicontinuity and cliquishness points of a real function $f$ of real variable, respectively.