How to type Logic Symbol in Pages?
You could also import a file like this to TextExpander:

not,¬
or,∨
and,∧
l,←
r,→
lr,↔
ll,⇐
rr,⇒
iff,⇔
all,∀
some,∃
nsome,∄
neq,≠
xor,⊻
nand,⊼
nor,⊽
oplus,⊕
qed,∎
equiv,≡
top,⊤
bot,⊥
vdash,⊢
models,⊨
nmodels,⊭


I made a text file for HTML5 entity names based on http://www.w3.org/TR/xml-entity-names/byalpha.html. Many of the abbreviations are the same as TeX / LaTeX character commands.