diff --git a/Sources/ArgumentParser/CMakeLists.txt b/Sources/ArgumentParser/CMakeLists.txt
index 2a65d2262..bace0ad5e 100644
--- a/Sources/ArgumentParser/CMakeLists.txt
+++ b/Sources/ArgumentParser/CMakeLists.txt
@@ -23,7 +23,6 @@ add_library(ArgumentParser
   Parsing/ArgumentDecoder.swift
   Parsing/ArgumentDefinition.swift
   Parsing/ArgumentSet.swift
-  Parsing/ArgumentSetSequence.swift
   Parsing/CommandParser.swift
   Parsing/InputOrigin.swift
   Parsing/Name.swift
diff --git a/Sources/ArgumentParser/Parsable Properties/Argument.swift b/Sources/ArgumentParser/Parsable Properties/Argument.swift
index dea1b7d76..69a55ab41 100644
--- a/Sources/ArgumentParser/Parsable Properties/Argument.swift	
+++ b/Sources/ArgumentParser/Parsable Properties/Argument.swift	
@@ -280,8 +280,8 @@ extension Argument {
           values.set(v, forKey: key, inputOrigin: origin)
         }
       })
-      return ArgumentSet(alternatives: [arg])
-      })
+      return ArgumentSet(arg)
+    })
   }
 
   /// Creates a property that reads its value from an argument, parsing with
@@ -403,7 +403,7 @@ extension Argument {
         update: .appendToArray(forType: Element.self, key: key),
         initial: setInitialValue)
       arg.help.defaultValue = helpDefaultValue
-      return ArgumentSet(alternatives: [arg])
+      return ArgumentSet(arg)
     })
   }
 
@@ -501,7 +501,7 @@ extension Argument {
         }),
         initial: setInitialValue)
       arg.help.defaultValue = helpDefaultValue
-      return ArgumentSet(alternatives: [arg])
+      return ArgumentSet(arg)
     })
   }
 
diff --git a/Sources/ArgumentParser/Parsable Properties/Flag.swift b/Sources/ArgumentParser/Parsable Properties/Flag.swift
index 1cba8becf..d7d313fd3 100644
--- a/Sources/ArgumentParser/Parsable Properties/Flag.swift	
+++ b/Sources/ArgumentParser/Parsable Properties/Flag.swift	
@@ -400,9 +400,7 @@ extension Flag where Value: EnumerableFlag {
           hasUpdated = try ArgumentSet.updateFlag(key: key, value: value, origin: origin, values: &values, hasUpdated: hasUpdated, exclusivity: exclusivity)
         }))
       }
-      return exclusivity == .exclusive
-        ? ArgumentSet(exclusive: args)
-        : ArgumentSet(additive: args)
+      return ArgumentSet(args)
       })
   }
 
@@ -525,9 +523,7 @@ extension Flag {
         }))
 
       }
-      return exclusivity == .exclusive
-        ? ArgumentSet(exclusive: args)
-        : ArgumentSet(additive: args)
+      return ArgumentSet(args)
       })
   }
 
@@ -553,7 +549,7 @@ extension Flag {
           })
         }))
       }
-      return ArgumentSet(additive: args)
+      return ArgumentSet(args)
     })
   }
 
@@ -628,9 +624,7 @@ extension Flag where Value: CaseIterable, Value: RawRepresentable, Value: Equata
           hasUpdated = try ArgumentSet.updateFlag(key: key, value: value, origin: origin, values: &values, hasUpdated: hasUpdated, exclusivity: exclusivity)
         }))
       }
-      return exclusivity == .exclusive
-        ? ArgumentSet(exclusive: args)
-        : ArgumentSet(additive: args)
+      return ArgumentSet(args)
       })
   }
 }
@@ -656,9 +650,7 @@ extension Flag {
           hasUpdated = try ArgumentSet.updateFlag(key: key, value: value, origin: origin, values: &values, hasUpdated: hasUpdated, exclusivity: exclusivity)
         }))
       }
-      return exclusivity == .exclusive
-        ? ArgumentSet(exclusive: args)
-        : ArgumentSet(additive: args)
+      return ArgumentSet(args)
     })
   }
   
@@ -686,7 +678,7 @@ extension Flag {
           })
         }))
       }
-      return ArgumentSet(additive: args)
+      return ArgumentSet(args)
     })
   }
 }
diff --git a/Sources/ArgumentParser/Parsable Properties/Option.swift b/Sources/ArgumentParser/Parsable Properties/Option.swift
index adc1f52f8..c4851cffa 100644
--- a/Sources/ArgumentParser/Parsable Properties/Option.swift	
+++ b/Sources/ArgumentParser/Parsable Properties/Option.swift	
@@ -391,7 +391,7 @@ extension Option {
       })
       arg.help.options.formUnion(ArgumentDefinition.Help.Options(type: Value.self))
       arg.help.defaultValue = initial.map { "\($0)" }
-      return ArgumentSet(alternatives: [arg])
+      return ArgumentSet(arg)
       })
   }
 
@@ -534,7 +534,7 @@ extension Option {
         initial: setInitialValue
       )
       arg.help.defaultValue = helpDefaultValue
-      return ArgumentSet(alternatives: [arg])
+      return ArgumentSet(arg)
     })
   }
 
@@ -636,7 +636,7 @@ extension Option {
         initial: setInitialValue
       )
       arg.help.defaultValue = helpDefaultValue
-      return ArgumentSet(alternatives: [arg])
+      return ArgumentSet(arg)
     })
   }
 
diff --git a/Sources/ArgumentParser/Parsable Types/ParsableArguments.swift b/Sources/ArgumentParser/Parsable Types/ParsableArguments.swift
index e7fe0686d..25fedcfcb 100644
--- a/Sources/ArgumentParser/Parsable Types/ParsableArguments.swift	
+++ b/Sources/ArgumentParser/Parsable Types/ParsableArguments.swift	
@@ -237,7 +237,7 @@ extension ArgumentSet {
         let key = InputKey(rawValue: codingKey)
         return parsed.argumentSet(for: key)
     }
-    self.init(additive: a)
+    self.init(sets: a)
   }
 }
 
diff --git a/Sources/ArgumentParser/Parsable Types/ParsableArgumentsValidation.swift b/Sources/ArgumentParser/Parsable Types/ParsableArgumentsValidation.swift
index 2a26ab39c..bbbb9dbae 100644
--- a/Sources/ArgumentParser/Parsable Types/ParsableArgumentsValidation.swift	
+++ b/Sources/ArgumentParser/Parsable Types/ParsableArgumentsValidation.swift	
@@ -55,21 +55,11 @@ extension ParsableArguments {
 
 fileprivate extension ArgumentSet {
   var firstPositionalArgument: ArgumentDefinition? {
-    switch content {
-    case .arguments(let arguments):
-      return arguments.first(where: { $0.isPositional })
-    case .sets(let sets):
-      return sets.first(where: { $0.firstPositionalArgument != nil })?.firstPositionalArgument
-    }
+    content.first(where: { $0.isPositional })
   }
   
   var firstRepeatedPositionalArgument: ArgumentDefinition? {
-    switch content {
-    case .arguments(let arguments):
-      return arguments.first(where: { $0.isRepeatingPositional })
-    case .sets(let sets):
-      return sets.first(where: { $0.firstRepeatedPositionalArgument != nil })?.firstRepeatedPositionalArgument
-    }
+    content.first(where: { $0.isRepeatingPositional })
   }
 }
 
@@ -234,13 +224,8 @@ struct ParsableArgumentsUniqueNamesValidator: ParsableArgumentsValidator {
     }
 
     let countedNames: [String: Int] = argSets.reduce(into: [:]) { countedNames, args in
-      switch args.content {
-      case .arguments(let defs):
-        for name in defs.flatMap({ $0.names }) {
-          countedNames[name.synopsisString, default: 0] += 1
-        }
-      default:
-        break
+      for name in args.content.flatMap({ $0.names }) {
+        countedNames[name.synopsisString, default: 0] += 1
       }
     }
 
diff --git a/Sources/ArgumentParser/Parsing/ArgumentSet.swift b/Sources/ArgumentParser/Parsing/ArgumentSet.swift
index 40e84d689..606c4b7ed 100644
--- a/Sources/ArgumentParser/Parsing/ArgumentSet.swift
+++ b/Sources/ArgumentParser/Parsing/ArgumentSet.swift
@@ -19,74 +19,38 @@
 /// The `-v | -f` part is one *set* that’s optional, `<input> <output>` is
 /// another. Both of these can then be combined into a third set.
 struct ArgumentSet {
-  enum Content {
-    /// A leaf list of arguments.
-    case arguments([ArgumentDefinition])
-    /// A node with additional `[ArgumentSet]`
-    case sets([ArgumentSet])
-  }
-  var content: Content
-  var kind: Kind
+  var content: [ArgumentDefinition] = []
+  var namePositions: [Name: Int] = [:]
   
-  /// Used to generate _help_ text.
-  enum Kind {
-    /// Independent
-    case additive
-    /// Mutually exclusive
-    case exclusive
-    /// Several ways of achieving the same behavior. Should only display one.
-    case alternatives
+  init<S: Sequence>(_ arguments: S) where S.Element == ArgumentDefinition {
+    self.content = Array(arguments)
+    self.namePositions = Dictionary(
+      content.enumerated().flatMap { i, arg in arg.names.map { ($0, i) } },
+      uniquingKeysWith: { first, _ in first })
   }
   
-  init(arguments: [ArgumentDefinition], kind: Kind) {
-    self.content = .arguments(arguments)
-    self.kind = kind
-  }
+  init() {}
   
-  init(sets: [ArgumentSet], kind: Kind) {
-    self.content = .sets(sets)
-    self.kind = kind
+  init(_ arg: ArgumentDefinition) {
+    self.init([arg])
+  }
+
+  init(sets: [ArgumentSet]) {
+    self.init(sets.joined())
   }
 }
 
 extension ArgumentSet: CustomDebugStringConvertible {
   var debugDescription: String {
-    switch content {
-    case .arguments(let args):
-      return args
-        .map { $0.debugDescription }
-        .joined(separator: " / ")
-    case .sets(let sets):
-      return sets
-        .map { "{\($0.debugDescription)}" }
-        .joined(separator: " / ")
-    }
+    content
+      .map { $0.debugDescription }
+      .joined(separator: " / ")
   }
 }
 
-extension ArgumentSet {
-  init() {
-    self.init(arguments: [], kind: .additive)
-  }
-  
-  init(_ arg: ArgumentDefinition) {
-    self.init(arguments: [arg], kind: .additive)
-  }
-  
-  init(additive args: [ArgumentDefinition]) {
-    self.init(arguments: args, kind: .additive)
-  }
-  
-  init(exclusive args: [ArgumentDefinition]) {
-    self.init(arguments: args, kind: args.count == 1 ? .additive : .exclusive)
-  }
-  
-  init(alternatives args: [ArgumentDefinition]) {
-    self.init(arguments: args, kind: args.count == 1 ? .additive : .alternatives)
-  }
-  
-  init(additive sets: [ArgumentSet]) {
-    self.init(sets: sets, kind: .additive)
+extension ArgumentSet: Sequence {
+  func makeIterator() -> Array<ArgumentDefinition>.Iterator {
+    return content.makeIterator()
   }
 }
 
@@ -150,7 +114,7 @@ extension ArgumentSet {
     let disableArg = ArgumentDefinition(kind: .named(disableNames), help: ArgumentDefinition.Help(options: [.isOptional], key: key), completion: .default, update: .nullary({ (origin, name, values) in
         hasUpdated = try ArgumentSet.updateFlag(key: key, value: false, origin: origin, values: &values, hasUpdated: hasUpdated, exclusivity: exclusivity)
     }), initial: { _, _ in })
-    return ArgumentSet(exclusive: [enableArg, disableArg])
+    return ArgumentSet([enableArg, disableArg])
   }
   
   /// Creates an argument set for an incrementing integer flag.
@@ -390,7 +354,7 @@ extension ArgumentSet {
   func first(
     matching parsed: ParsedArgument
   ) -> ArgumentDefinition? {
-    return first(where: { $0.names.contains(parsed.name) })
+    namePositions[parsed.name].map { content[$0] }
   }
   
   func firstPositional(
diff --git a/Sources/ArgumentParser/Parsing/ArgumentSetSequence.swift b/Sources/ArgumentParser/Parsing/ArgumentSetSequence.swift
deleted file mode 100644
index 6287b38d1..000000000
--- a/Sources/ArgumentParser/Parsing/ArgumentSetSequence.swift
+++ /dev/null
@@ -1,63 +0,0 @@
-//===----------------------------------------------------------*- swift -*-===//
-//
-// This source file is part of the Swift Argument Parser open source project
-//
-// Copyright (c) 2020 Apple Inc. and the Swift project authors
-// Licensed under Apache License v2.0 with Runtime Library Exception
-//
-// See https://swift.org/LICENSE.txt for license information
-//
-//===----------------------------------------------------------------------===//
-
-/// Allows iteration over arguments in an `ArgumentSet`.
-extension ArgumentSet: Sequence {
-  func makeIterator() -> Iterator {
-    return Iterator(set: self)
-  }
-  
-  var underestimatedCount: Int { return 0 }
-  
-  struct Iterator: IteratorProtocol {
-    enum Content {
-      case arguments(ArraySlice<ArgumentDefinition>)
-      case sets([Iterator])
-      case empty
-    }
-    
-    var content: Content
-    
-    init(set: ArgumentSet) {
-      switch set.content {
-      case .arguments(let a):
-        self.content = .arguments(a[a.startIndex..<a.endIndex])
-      case .sets(let sets):
-        self.content = .sets(sets.map {
-          $0.makeIterator()
-        })
-      }
-    }
-    
-    mutating func next() -> ArgumentDefinition? {
-      switch content {
-      case .arguments(var a):
-        guard !a.isEmpty else { return nil }
-        let n = a.remove(at: 0)
-        content = .arguments(a)
-        return n
-      case .sets(var sets):
-        defer {
-          content = .sets(sets)
-        }
-        while true {
-          guard !sets.isEmpty else { return nil }
-          if let n = sets[0].next() {
-            return n
-          }
-          sets.remove(at: 0)
-        }
-      case .empty:
-        return nil
-      }
-    }
-  }
-}
diff --git a/Sources/ArgumentParser/Parsing/Name.swift b/Sources/ArgumentParser/Parsing/Name.swift
index 267d9e48d..cd940d9ca 100644
--- a/Sources/ArgumentParser/Parsing/Name.swift
+++ b/Sources/ArgumentParser/Parsing/Name.swift
@@ -9,7 +9,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-enum Name: Equatable {
+enum Name: Hashable {
   /// A name (usually multi-character) prefixed with `--` (2 dashes) or equivalent.
   case long(String)
   /// A single character name prefixed with `-` (1 dash) or equivalent.
diff --git a/Sources/ArgumentParser/Usage/UsageGenerator.swift b/Sources/ArgumentParser/Usage/UsageGenerator.swift
index 05f844ecd..d8d18d89b 100644
--- a/Sources/ArgumentParser/Usage/UsageGenerator.swift
+++ b/Sources/ArgumentParser/Usage/UsageGenerator.swift
@@ -27,7 +27,7 @@ extension UsageGenerator {
   }
   
   init(toolName: String, definition: [ArgumentSet]) {
-    self.init(toolName: toolName, definition: ArgumentSet(additive: definition))
+    self.init(toolName: toolName, definition: ArgumentSet(sets: definition))
   }
 }