Intervals merge problem in F#, run with `dotnet fsi intervals.fsx`

intervals.fsx

//Run with `dotnet fsi intervals.fsx`
let intervals = [|
    (1,3)
    (12,15)
    (23, 41)
    (8,10)
    (2,6)
    (13,21)
    (20,21)
    (14,22)
|]

let output = [|
    (1,6)
    (8,10)
    (12,22)
    (23,41)
|]

let overlaps (int1:int*int) (int2:int*int) :bool =
    fst int1 >= fst int2 && fst int1 <= snd int2
    
let mergeIntervals iis =
    if (iis |> Array.length) = 1 then
        iis
    else
        let sortedInput = Array.sortBy (fst) iis
        let result = ResizeArray(capacity=iis.Length)
        result.Add(iis[0])
        for i in 1..sortedInput.Length-1 do
            let current = sortedInput[i]
            let lastInterval = result |> Seq.last
            if overlaps current lastInterval then
                result[result.Count - 1] <- (
                             min (fst current) (fst lastInterval),
                             max (snd current) (snd lastInterval)
                            )
//                result.RemoveAt(result.Count - 1)
//                result.Add(
//                            (
//                             min (fst current) (fst lastInterval),
//                             max (snd current) (snd lastInterval)
//                            )
//                          )
            else
                result.Add current
        result.ToArray()
    
let actual = mergeIntervals intervals
printfn $"Input: %A{intervals}"
printfn $"Output: %A{actual}"
printfn $"Actual = expected {actual = output}"