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Minimal Basically Disconnected Covers of P'-spaces
정갑헌,김창일 영남수학회 2014 East Asian mathematical journal Vol.30 No.1
Observing that for any P0-space X, vX is a P0-space if vX is a weakly Lindelof space, (vXY;X Y ) is the minimal basically disconnected cover of XY for a countably locally weakly Lindelof space Y .
Minimal quasi-F covers of some extension
김창일,정갑헌 충청수학회 2013 충청수학회지 Vol.26 No.2
Observing that every Tychonoff space X has an extension kX which is a weakly LindelÄof space and the minimal quasi-F cover QF(kX) of kX is a weakly LindelÄof, we show that ΦkX :QF(kX) → kX is a z#-irreducible map and that QF(βX)=βQF(kX). Using these, we prove that QF(kX) = kQF(X) if and only if ΦkX : kQF(X) → kX is an onto map and βQF(X) =QF(βX).
STABILITY OF A CUBIC FUNCTIONAL EQUATION IN 2-NORMED SPACES
김창일,정갑헌 한국전산응용수학회 2014 Journal of applied mathematics & informatics Vol.32 No.5
In this paper, we prove the generalized Hyers-Ulam stability of the following cubic funtional equation f(2x + y) + f(2x −y) = 2f(x + 2y) −4f(x + y) + 18f(x) −12f(y) by the direct method in 2-normed spaces.