If I made no mistakes ##\lambda = \ln(2)##
I thought it was basic because it was mentioned in my probability theory book from my university, but it does mention that the proof is not trivial. So maybe basic theorem, but certainly not a basic proof. I also don't seem to find a good source to back up. When university starts again, I will ask my probability prof for a reference.So?
Could you give a quotation of this "basic result"?