General help

I suspect my problem is not really moodle-related, but in the hope that someone has run into a similar issue and will be able to offer advice, I'll post it here:

Some teachers at our university use special characters for logical symbols, eg:

• p∧­q
• p∨­q
• p⇒­q
• p⇔q

They do this by inserting appropriate html entities in the post. However, some students can't view those special characters. Instead, they see some rectangles. Does anyone know what might be causing the problem and how I can fix this?

Thanks in advance,
Przemek