List Remove trick

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type System.Collections.Generic.List<'T> with
  member this.RemoveAtUnordered(index:int) =
    this.[index] <- this.[this.Count-1]
    this.RemoveAt(this.Count-1)
  member this.RemoveUnordered(item:'T) =
    let index = this.IndexOf(item)
    if index <> - 1 then this.RemoveAt(index)

namespace System

namespace System.Collections

namespace System.Collections.Generic

Multiple items
type List<'T> =
  new : unit -> List<'T> + 2 overloads
  member Add : item:'T -> unit
  member AddRange : collection:IEnumerable<'T> -> unit
  member AsReadOnly : unit -> ReadOnlyCollection<'T>
  member BinarySearch : item:'T -> int + 2 overloads
  member Capacity : int with get, set
  member Clear : unit -> unit
  member Contains : item:'T -> bool
  member ConvertAll<'TOutput> : converter:Converter<'T, 'TOutput> -> List<'TOutput>
  member CopyTo : array:'T[] -> unit + 2 overloads
  ...
  nested type Enumerator

Full name: System.Collections.Generic.List<_>

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System.Collections.Generic.List() : unit
System.Collections.Generic.List(capacity: int) : unit
System.Collections.Generic.List(collection: System.Collections.Generic.IEnumerable<'T>) : unit

val this : System.Collections.Generic.List<'T>

member System.Collections.Generic.List.RemoveAtUnordered : index:int -> unit

Full name: Script.RemoveAtUnordered

val index : int

Multiple items
val int : value:'T -> int (requires member op_Explicit)

Full name: Microsoft.FSharp.Core.Operators.int

--------------------
type int = int32

Full name: Microsoft.FSharp.Core.int

--------------------
type int<'Measure> = int

Full name: Microsoft.FSharp.Core.int<_>

property System.Collections.Generic.List.Count: int

System.Collections.Generic.List.RemoveAt(index: int) : unit

member System.Collections.Generic.List.RemoveUnordered : item:'T -> unit

Full name: Script.RemoveUnordered

val item : 'T

System.Collections.Generic.List.IndexOf(item: 'T) : int
System.Collections.Generic.List.IndexOf(item: 'T, index: int) : int
System.Collections.Generic.List.IndexOf(item: 'T, index: int, count: int) : int