HTML coverage — freeform answer
State and prove the summation formula $\sum_{i=1}^{n} i = \tfrac{n(n+1)}{2}$. This fixture
exercises the Markdown-rendered freeform answer path.
Answer & solution
Answer
Prove by induction. Base case: $n=1$ gives $1 = 1$. Step: assume the identity
holds for $n=k$; adding $k+1$ to both sides establishes it for $n=k+1$.