def foo
  puts 'foo'
end

for nice in this:
    print "how interesting"

\[ 
\sum_{n=1}^\infty \frac{1}{n} 
\text{ is divergent, but } 
\lim_{n \to \infty} \sum_{i=1}^n \frac{1}{i} - \ln n \text{exists.} 
\]