Testing the isset() function:
$var1 set? false
$var2 set? false
$var3 set? true
$var4 set? true
$var5 set? true
$var6 set? true
$var7 set? true
$var8 set? false
$var9 set? true

Testing the empty() function:
$var_1 empty? true
$var_2 empty? true
$var_3 empty? true
$var_4 empty? true
$var_5 empty? true
$var_6 empty? true
$var_7 empty? true
$var_8 empty? true
$var_9 empty? true