[8140david]

Thanks for the information.

In my epub and on the Kobo Aura, the mathematical symbols that are shown as a box are:
∧ ∧
∨ ∨
∃ ∃
∀ ∀

The mathematical symbols that are shown correctly are:
→ →
↔ ↔
≡ ≡
≤ ≤
&lt; <

In the "epub feature peeker" provided in the forum, it says:
For instance the character 'Latin small letter s with cedilla', namely ş, has the Unicode code point U+015F, and can be encoded in your epub with:
Hexadecimal: &#x015f;
Decimal: ş

So should I use the unicode code for mathematical symbols?
Here are the codes of the symbols that interest me:
http://en.wikipedia.org/wiki/Mathematical_Operators
(NB: This page indicates 3 different codings of characters, as entity, num entity, and hex entity:
http://symbolcodes.tlt.psu.edu/bylan...mathchart.html)

For the 4 problematic symbols above, the Unicodes are respectively:
U+2227 ∧
U+2228 ∨
U+2203 ∃
U+2200 ∀

So the html coding should be this, for the first one?
&#x2227; ∧
I'll try it.