``Document markup'' languages

I need some efficient, quick and simple way to enter advanced mathematical formulae in between text (that can be nicely formatted), is LaTeX a nice way to do it? Please recommend me something decent.

Troff with eqn is very nice.


.EQ
sum from { i=1 } to inf e sup { 2i }
.EN

A famous equation is $e sup { i pi } = -1$ .


.EQ
define exists '~\(te~'
define suchthat '~:~'
define forall '~\(fa~'
define member '~\(mo~'
exists a sub mu member bold Z
suchthat a sub mu < delta
forall delta member bold Z
.EN


.EQ
define dne !~ \o'/\(te' ~!
dne beta member bold N
suchthat beta > THETA
forall THETA member bold Z
.EN