I’m trying to track down a Dave Parnas quote - apparently he said something like “You can’t get from the informal to the formal by formal means.” I think it was in the context of his work “A rational design process: How and Why to fake it”. Does anyone know or have an idea where I could look to find it?

The quote is attributed to Alan Perlis, but maybe he was quoting someone else. "One can't proceed from the informal to the formal by formal means." From "Epigrams in Programming" by Alan Perlis, ACM SIGPLAN Notices, September 1982.

iirc David Mackenzie talks about this in Mechanizing Proof; Perlis felt that mechanized proof proceeded from the informal to the formal by formal means.

@Doug Moen - thanks. http://www.cs.yale.edu/homes/perlis-alan/quotes.html