I am the smallest of all Math symbol you can find. I cannot be left alone or I will perish! I must always be sandwiched between 2 numbers. If nothing of value appears on my left, I require my rolly-polly bodyguard to stand on my left. If nothing of value appears on my right, a rolly-polly bodyguard need to stand on my right, else I will have to take my leave. What am I?