"It is well known" is a weasel word, and hence requires more substantiation when asked. If one has to rely on Googling on these matters, one can find so many co

"It is well known" is a weasel word, and hence requires more substantiation when asked. If one has to rely on Googling on these matters, one can find so many contradictory views. So I wanted to know what reputed sources the GP was relying on to use "It is well known" for that claim.