You probably meant ∑ (\sum) rather than Σ (\Sigma). The two are different symbols, and they are sometimes used in the same expressions. For example, in the fiel

You probably meant ∑ (\sum) rather than Σ (\Sigma). The two are different symbols, and they are sometimes used in the same expressions. For example, in the field I (used to) work, a sum over all characters in the alphabet would be written as \sum_{c \in \Sigma}. Mathematical syntax is complex, and the typesetting often becomes unreadable outside trivial cases. Using Unicode won't help much, especially because it's easy to confuse similar-looking but unrelated symbols. Proper syntax highlighting might help, but I've never seen a tool doing a good job with it.