After 1.Nf3 d5 2.c4 there is not much to be found in Reti literature concerning the move 2...Nf6. Below is the only mention of it I have found which I have reproduced as closely as possible:
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Chess Opening
Essentials
Djuric - Komarov - Pantaleoni
2010
vol 4 pg 37
Reti Opening
1.f3 d5 2.c4
We will now have a look at the specifics of the Reti Opening.
"In addition to the four alternatives that we are about to examine, there is the dubious
2...f6, which is curiously common at lower levels.
After 3.cxd5 xd5 4.e4
(or 4.d4) there is no knight on c3 to capture, and White conquers the centre without having to worry about the typical counterplay that Black has with the Grunfeld and the Semi-Tarrasch."
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Chess Opening