Can you provide any failed attempts to prove that ZF or ZFC to be inconsistent?


References to articles in the literature if there are any will be much appreciated.


Thanks!



Which failed attempts have there been to find a contradiction in ZFC or ZF?
I think the most noticeable one was Nelson's attempt to prove the inconsistency of primitive recursive arithmetic. Terence Tao found a mistake in the proof, but Nelson's attempt was posthumously uploaded to arxiv (<https://arxiv.org/pdf/1509.09209.pdf>), together with an introduction by Sarah Jones Nelson and an afterword by Sam Buss and Terence Tao himself. 


Nelson was amongst the very few serious mathematicians who supported the view that arithmetic was indeed inconsistent, based on his ultrafinitist philosophy.


