Jonathan Graham, the former head of Citadel’s quantitative-investing unit, is laying the groundwork for his own investment business.Word began to spread in the past few weeks after his non-compete agreement with Citadel expired. Graham left the $31 billion multi-strategy fund manager in March 2017.It’s unclear when Graham hopes to launch, or exactly what type of business he envisions. But his efforts are of keen interest to quant...