I first asked about the dev system and got a rock-solid affirmative answer that all was good at that point: all values check out and are consistent. So I went module-by-module until things didn't make sense. I started writing basically principles of math on the board to share what was being said in response to my questions. The associative law was being violated: A=B and B=C but A!=C. Hmmm. Finally I was being told, in effect, C!=C. I went back to square and step one and found out, ah-ha! The interviewer had lied. The values were not consistent and do change. I back tracked to get us onto common language and found out not only was this misleading, but the domain language - which I knew - was being used incorrectly in the problem even though the person had written systems for this domain for 2 years. I've been in software for almost 2 decades and have interviewed dozens of people and likewise been interviewed dozens of times. This was the most surreal and bizarre interview I've ever had in my life. Logic was out the window. I solved the "problem" (turns out there wasn't a real problem, the interviewer just wanted to "share" the stress from work) and felt I'd gone into a Lewis Carroll story and was through the looking glass.