(3) cg(f¡1¡cg¡ig(F)¢¢) j f¡1(F) for every g-closed subset F in Y .
(4) cg(f¡1(cg¡cg()) j f¡1¡cg(B)¢for every subset B in Y .
(5) f¡1¡ig(B)¢j ig(f¡1(ig¡ig(B)¢¢)) for every subset B in Y .
(6) For every gr-open subset V in Y , f¡1(V ) is g-open.
(7) For every gr-closed subset F in Y , f¡1(F) is g-closed.
Proof. (1) ) (2). Let V be a g-open set in Y and x 2 f¡1(V ).
Thereexists a g-open set U of X containing x such that f(U) j ig¡cg(V )¢.
Thisimplies x 2 ig(f¡ig¡cg(¢¢). Hence f¡1(V ) j ig(f¡1¡ig¡cg(¢¢).(2) ) (3). Let F be a g-closed set in Y . From Theorem 2.1,
it followsf¡1(Y ¡ F) j ig(f¡1¡ig¡cg(Y ¡ F)¢¢)= ig(f¡1¡Y ¡ cg¡ig(¢¢) = X ¡ cg(f¡¡ig(F)¢¢):
Hence cg(f¡1¡cg¡ig(F)¢¢) j f¡1(F).
(3) ) (4). It is obvious.
(4) ) (5). It follows from Theorem 2.1.
(5) ) (6). Let V be any gr-open set of Y . Since ig(ig(¢) = from (5), it follows f¡1(V ) j ig¡f¡1(and so f¡1(V ) =f¡1(V )¢.
(6) ) (7). Let F be any gr-closed set of Y . Then by (6), we have