I don't think we have enough information about the nature of DG's business relationship with AL to know if the grudge is "petty" or not.
If AL had an idea for a pump and designed the thing, it's possible he hired DG to wire it for him. That doesn't make the pump DG's idea or his creation. For example, if AL designed a pump, and approached DG, saying "I'll pay you $500 to wire this pump for me" - that just indicates to me that DG was hired to perform a job. In this case, IMO, DG's grudge is indeed "petty".
On the other hand, if AL says to DG, I want to design a particular kind of pump for a particular purpose, you're a smart guy, let's work on this together, they both come up with the idea, and create the pump, that is partly DG's invention and his name should be on the patent.
We don't know the extent to which DG contributed intellectually to the whole pump idea. We only know he was hired to wire it.
It would be interesting if someone familiar with patent law could weigh in.
And, in my own opinion, the fact the pump turned out to be basically worthless, no one profited from it, the idea was shelved, yet DG still held a grudge for many years, culminating in triple murder, yeah, I'd say it was a petty grudge that did not warrant a murderous rage.
IMO
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