None of the many Kobo installed fonts had all the math characters I needed in some recently added documents. In particular, they all lacked most or all of Quine Quotes, the semantic and syntactic turnstile relations, and the modal logic necessity box.
So for example, these cannot be rendered:
If PA ⊢ A, then PA ⊢ Prov(⌈A⌉);
□(□A → A) → □A
if Γ ⊨ θ, then Γ ⊢ θ.
I found a font from the GNU project which has these characters in it which is not too bad:
http://www.gnu.org/software/freefont/
Maybe there are some others around too?