Title of article :
Closed maps on spaces with point-countable bases
Author/Authors :
Tsugunori and Shibakov، نويسنده , , Alexander، نويسنده ,
Issue Information :
دوماهنامه با شماره پیاپی سال 1999
Abstract :
We prove a version of Lašnevʹs theorem for spaces with point-countable bases.
m. Let X have a point-countable base, f:X→Y be a closed map. Then there is an ω1-relatively-discrete subspace Z of Y such that |Z|≤d(Y) and f−1(y) is compact for every y∈Y\Z.
e study the subspaces of closed images of regular spaces with point-countable bases and show that every such subspace has countable π-character and a point-countable π-base. The latter result is extended to a wider class of spaces which is invariant under closed maps and products with metrizable compacta. The proofs use a structure which controls the convergence properties of the space and those of its closed image.
Keywords :
?-character , Point-countable base , Sequential order , ?-base , Closed map , Sequential space , La?nevיs theorem
Journal title :
Topology and its Applications
Journal title :
Topology and its Applications