$ cd `mktemp -d`
$ mkdir one
$ mkdir two
$ chmod -R 755 .
$ touch one/foo
$ chmod 0 one/foo
$ cat one/foo
cat: one/foo: Permission denied
$ mv -v one/foo two/
‘one/foo’ -> ‘two/foo’
$ chmod a-w one
$ mv -v two/foo one/
‘two/foo’ -> ‘one/foo’
mv: cannot move ‘two/foo’ to ‘one/foo’: Permission denied
$ chmod u+w one
$ chmod a-w two
$ mv -v two/foo one/
‘two/foo’ -> ‘one/foo’
mv: cannot move ‘two/foo’ to ‘one/foo’: Permission denied
$ chmod u+w two
$ mv -v two/foo one/
‘two/foo’ -> ‘one/foo’