diff --git a/prototype/Doubt/Patch.swift b/prototype/Doubt/Patch.swift
index 057694d1b..ac9c15fb7 100644
--- a/prototype/Doubt/Patch.swift
+++ b/prototype/Doubt/Patch.swift
@@ -16,17 +16,6 @@ public enum Patch<A>: CustomDebugStringConvertible, CustomDocConvertible {
 	}
 
 
-	/// The cost of a patch to the diff.
-	public var cost: Int {
-		switch self {
-		case .Replace:
-			return 2
-		default:
-			return 1
-		}
-	}
-
-
 	public var inverse: Patch {
 		switch self {
 		case let .Replace(a, b):
diff --git a/prototype/Doubt/SES.swift b/prototype/Doubt/SES.swift
index 847b84434..93404de5a 100644
--- a/prototype/Doubt/SES.swift
+++ b/prototype/Doubt/SES.swift
@@ -8,7 +8,7 @@ public func SES<Term, A>(a: [Term], _ b: [Term], recur: (Term, Term) -> Free<A,
 	if b.isEmpty { return a.map { Diff.Pure(Patch.Delete($0)) } }
 
 	func cost(diff: Diff) -> Int {
-		return diff.map { $0.cost }.iterate { syntax in
+		return diff.map(const(1)).iterate { syntax in
 			switch syntax {
 			case .Leaf:
 				return 0
@@ -75,4 +75,5 @@ public func SES<Term, A>(a: [Term], _ b: [Term], recur: (Term, Term) -> Free<A,
 
 
 import Memo
+import Prelude
 import Stream
diff --git a/prototype/UI/Fixtures/swift.json b/prototype/UI/Fixtures/swift.json
index d72eceb71..14c8b4fe7 100644
--- a/prototype/UI/Fixtures/swift.json
+++ b/prototype/UI/Fixtures/swift.json
@@ -1,68 +1,13 @@
-[
-	[{
-			"source": "Algorithm",
-			"categories": [
-
-			]
-		},
-		[
-			[{
-					"source": "Recursive",
-					"categories": [
-
-					]
-				},
-				[
-
-				]
-			],
-			[{
-					"source": "ByKey",
-					"categories": [
-
-					]
-				},
-				[
-
-				]
-			], {
-				"insert": [{
-						"source": "ByIndex",
-						"categories": [
-
-						]
-					},
-					[
-
-					]
-				]
-			}, {
-				"source": "mark",
-				"categories": [
-
-				]
-			},
-			[{
-					"source": "map(_:)",
-					"categories": [
-
-					]
-				},
-				[
-
-				]
-			]
-		]
-	], {
-		"insert": [{
-				"source": "FreeAlgorithm",
+[{
+		"delete": [{
+				"source": "Algorithm",
 				"categories": [
 
 				]
 			},
 			[
 				[{
-						"source": "Pure",
+						"source": "Recursive",
 						"categories": [
 
 						]
@@ -72,17 +17,7 @@
 					]
 				],
 				[{
-						"source": "Roll",
-						"categories": [
-
-						]
-					},
-					[
-
-					]
-				],
-				[{
-						"source": "analysis(ifPure:ifRoll:)",
+						"source": "ByKey",
 						"categories": [
 
 						]
@@ -104,31 +39,6 @@
 					},
 					[
 
-					]
-				], {
-					"source": "mark",
-					"categories": [
-
-					]
-				},
-				[{
-						"source": "flatMap(_:)",
-						"categories": [
-
-						]
-					},
-					[
-
-					]
-				],
-				[{
-						"source": "evaluate(_:recur:)",
-						"categories": [
-
-						]
-					},
-					[
-
 					]
 				]
 			]
@@ -142,14 +52,49 @@
 				]
 			},
 			"after": [{
-					"source": "FreeAlgorithm",
+					"source": "Algorithm",
 					"categories": [
 
 					]
 				},
 				[
 					[{
-							"source": "evaluate(_:)",
+							"source": "Recursive",
+							"categories": [
+
+							]
+						},
+						[
+
+						]
+					],
+					[{
+							"source": "ByKey",
+							"categories": [
+
+							]
+						},
+						[
+
+						]
+					],
+					[{
+							"source": "ByIndex",
+							"categories": [
+
+							]
+						},
+						[
+
+						]
+					], {
+						"source": "mark",
+						"categories": [
+
+						]
+					},
+					[{
+							"source": "map(_:)",
 							"categories": [
 
 							]
@@ -190,107 +135,125 @@
 				]
 			]
 		]
-	}, {
-		"delete": [{
-				"source": "FreeAlgorithm",
-				"categories": [
-
-				]
-			},
-			[
-				[{
-						"source": "Pure",
-						"categories": [
-
-						]
-					},
-					[
-
-					]
-				],
-				[{
-						"source": "Roll",
-						"categories": [
-
-						]
-					},
-					[
-
-					]
-				],
-				[{
-						"source": "analysis(ifPure:ifRoll:)",
-						"categories": [
-
-						]
-					},
-					[
-
-					]
-				], {
-					"source": "mark",
-					"categories": [
-
-					]
-				},
-				[{
-						"source": "map(_:)",
-						"categories": [
-
-						]
-					},
-					[
-
-					]
-				], {
-					"source": "mark",
-					"categories": [
-
-					]
-				},
-				[{
-						"source": "flatMap(_:)",
-						"categories": [
-
-						]
-					},
-					[
-
-					]
-				],
-				[{
-						"source": "evaluate(_:)",
-						"categories": [
-
-						]
-					},
-					[
-
-					]
-				]
-			]
-		]
-	}, {
-		"delete": [{
-				"source": "FreeAlgorithm",
-				"categories": [
-
-				]
-			},
-			[
-				[{
-						"source": "evaluate()",
-						"categories": [
-
-						]
-					},
-					[
-
-					]
-				]
-			]
-		]
 	},
+	[{
+			"source": "FreeAlgorithm",
+			"categories": [
+
+			]
+		},
+		[
+			[{
+					"source": "Pure",
+					"categories": [
+
+					]
+				},
+				[
+
+				]
+			],
+			[{
+					"source": "Roll",
+					"categories": [
+
+					]
+				},
+				[
+
+				]
+			],
+			[{
+					"source": "analysis(ifPure:ifRoll:)",
+					"categories": [
+
+					]
+				},
+				[
+
+				]
+			], {
+				"source": "mark",
+				"categories": [
+
+				]
+			},
+			[{
+					"source": "map(_:)",
+					"categories": [
+
+					]
+				},
+				[
+
+				]
+			], {
+				"source": "mark",
+				"categories": [
+
+				]
+			},
+			[{
+					"source": "flatMap(_:)",
+					"categories": [
+
+					]
+				},
+				[
+
+				]
+			],
+			[{
+					"replace": {
+						"before": {
+							"source": "evaluate(_:)",
+							"categories": [
+
+							]
+						},
+						"after": {
+							"source": "evaluate(_:recur:)",
+							"categories": [
+
+							]
+						}
+					}
+				},
+				[
+
+				]
+			]
+		]
+	],
+	[{
+			"source": "FreeAlgorithm",
+			"categories": [
+
+			]
+		},
+		[
+			[{
+					"replace": {
+						"before": {
+							"source": "evaluate()",
+							"categories": [
+
+							]
+						},
+						"after": {
+							"source": "evaluate(_:)",
+							"categories": [
+
+							]
+						}
+					}
+				},
+				[
+
+				]
+			]
+		]
+	],
 	[{
 			"source": "FreeConvertible",
 			"categories": [
@@ -338,36 +301,6 @@
 				]
 			}
 		]
-	],
-	[{
-			"source": "FreeAlgorithm",
-			"categories": [
-
-			]
-		},
-		[
-			[{
-					"source": "init(_:_:)",
-					"categories": [
-
-					]
-				},
-				[
-
-				]
-			], {
-				"insert": [{
-						"source": "evaluate(_:)",
-						"categories": [
-
-						]
-					},
-					[
-
-					]
-				]
-			}
-		]
 	], {
 		"insert": [{
 				"source": "FreeAlgorithm",
@@ -377,7 +310,17 @@
 			},
 			[
 				[{
-						"source": "evaluate()",
+						"source": "init(_:_:)",
+						"categories": [
+
+						]
+					},
+					[
+
+					]
+				],
+				[{
+						"source": "evaluate(_:)",
 						"categories": [
 
 						]
@@ -388,5 +331,34 @@
 				]
 			]
 		]
-	}
+	},
+	[{
+			"source": "FreeAlgorithm",
+			"categories": [
+
+			]
+		},
+		[
+			[{
+					"replace": {
+						"before": {
+							"source": "init(_:_:)",
+							"categories": [
+
+							]
+						},
+						"after": {
+							"source": "evaluate()",
+							"categories": [
+
+							]
+						}
+					}
+				},
+				[
+
+				]
+			]
+		]
+	]
 ]