print "undef  is ", ( undef  ) ? "true\n" : "false\n";
print "0      is ", ( 0      ) ? "true\n" : "false\n";
print "'0'    is ", ( '0'    ) ? "true\n" : "false\n";
print "''     is ", ( ''     ) ? "true\n" : "false\n";
print "' '    is ", ( ' '    ) ? "true\n" : "false\n";
print "'0.0'  is ", ( '0.0'  ) ? "true\n" : "false\n";
print "'0e00' is ", ( '0e00' ) ? "true\n" : "false\n";
__DATA__
undef  is false
0      is false
'0'    is false
''     is false
' '    is true
'0.0'  is true
'0e00' is true