A question that got me puzzled.
We know tuple syntax is used to pass arguments to/from .NET library methods from F#.
So no wonder both of these work:

#1

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let dict = new System.Collections.Generic.Dictionary<int, int>()
dict.Add (1, 2)

#2

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let dict = new System.Collections.Generic.Dictionary<int, int>()
let pair = (1, 2)


dict.Add pair

I was trying to use syntax #2 to call an overloaded library method:

#3

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let req = WebRequest.Create(url)
let header = ("name", "value")
req.Headers.Add header

Even though the type of header is well known, the compiler doesn't seem able to resolve the correct

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(string, string)

overload.
I get: No overloads match for method 'Add'. The available overloads are shown below.

This works fine:

#4

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let req = WebRequest.Create(url)
let 

header = ("name", "value")
req.Headers.Add (fst header, snd header)

Is this a bug, or a design choice? I'm using v. 1.9.7.8.
Cheers!