What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Thomas is not a doctor or Sarah is writing a letter. It is not overcast or it is sunny. If it is sunny, then Richard is fast. Thomas is a doctor or it is overcast. Sarah is writing a letter if and only if Richard is fast.
It is overcast or Sarah is writing a letter. If Sarah writes a letter, then Richard is fast. If Richard were fast, then Sarah is writing a letter.