Multiple unary operators in an if statement [duplicate]

Question

Is it possible to have multiple unary operators in if statements.. Here is the code snippet which is giving me error.

Please correct the code here.

if [ -f $input_file ] -a [ -f $output_file ] -a [ -f $log_file ] ]
then
    ### Some Code here
fi

Answer 1

if [ -f "file1" -a -f "file2" -a "file3" ]; then
   #some code
fi