Would a Russian First Use of Nuclear Weapons Inevitably Lead to a Nuclear Response?

Would a Russian first use of nuclear weapons inevitably in your view lead to a nuclear response? I don't want to go any details how NATO would react definitely there would be reaction because it would endanger NATO as such. See it's hard to imagine anything but more escalation given what you have said about a resolution needing to recognize Ukraine's sovereignty over all of its territory and of course that includes Crimea. Put that against what the Russians are saying about their determination by all means to keep their control over chunks of Ukrainian territory. We are on course are we not for that most dangerous escalation.