This week in Hilchos Shabbos shiur we learned about the machlokes haposkim as to whether ketchup is considered a dvar lach or yavesh in regards to reheating on Shabbos. Reb Moshe says it’s a d’var lach but still allows one to put ketchup on a hot potato or piece of meat because he maintains that bishul after bishul is a chumra and treating a solid hot substance as a kli rishon is also a chumra, and we don’t have to be machmir twice therefore one may place ketchup on a hot piece of shnitzel.