He thanked me for a certain letter which I had written to him as a matter of fact, I had offered him a job.
The job was the first one he has tried to work, and excelled at it. 
mnli hypothesis: The job was the first one he has tried to work, and excelled at it.  premise: He thanked me for a certain letter which I had written to him as a matter of fact, I had offered him a job.