deletions | additions       diff --git a/untitled.md b/untitled.md  index 4d009a5..ab5c671 100644  --- a/untitled.md  +++ b/untitled.md 
...
Problems to address:  * The fermion sign problem. How do FCIQMC and CCMC avoid it? The sign problem is NP-hard \cite{Troyer_2005} thus not solvable in polynomial time  TODO: