"is is"

[Mark A. Mandel]

James Landau writes:

>>>>>
P.S.  On a different topic.  I once perpetrated the following sentence: [In
reference to the Historia Matematica mailing list] "I thought that knowing
who Tartaglia is is a requirement for joining this list".  [Tartaglia was a
Medieval Italian mathematician.]  Is this sentence grammatical?  If so, then
it is possible to have the word "is" twice in a row without it having to be
in quotes.  However, it must be admitted that in response to that sentence I
received an e-mail from Germany politely requesting me to translate it into
English.
<<<<<

IMHO, grammatical beyond question, although prosodically somewhat challenging to the reader.

-- Mark A. Mandel