Conversation so far:
who's running for mayor of san francisco
Candidates running for mayor of San Francisco in the November 2019 election included Ellen Lee Zhou, Joel Ventresca, London Breed, Paul Ybarra Robertson, Robert Jordan, and Wilma Pang
why was the 2018 election for mayor of san francisco special
The 2018 San Francisco mayoral special election was called after former Mayor Ed Lee died on December 12, 2017.

Question: how
Self-contained rewrite: how did former mayor ed lee die