diff --git a/src/end-to-end.test.ts b/src/end-to-end.test.ts
index 7152b31..7ff9fe7 100644
--- a/src/end-to-end.test.ts
+++ b/src/end-to-end.test.ts
@@ -63,6 +63,10 @@ testCases(endToEnd, code => code)('end-to-end tests', [
   ['{ (a: :(")")), (")": (B)) }', either.makeRight({ a: 'B', ')': 'B' })],
   [':match({ a: A })({ tag: a, value: {} })', either.makeRight('A')],
   [':{string concatenate}(a)(b)', either.makeRight('ba')],
+  [
+    ':flow({ :string.concatenate(a) :string.concatenate(b) })(z)',
+    either.makeRight('zab'),
+  ],
   [
     `{
         "static data":"blah blah blah"
@@ -212,4 +216,12 @@ testCases(endToEnd, code => code)('end-to-end tests', [
       value: 'true',
     }),
   ],
+  [
+    `:integer.add(
+      :integer.subtract(1)(2)
+    )(
+      :integer.subtract(2)(4)
+    )`,
+    either.makeRight('3'),
+  ],
 ])
diff --git a/src/language/compiling/semantics/prelude.ts b/src/language/compiling/semantics/prelude.ts
index cdf099e..bf954d4 100644
--- a/src/language/compiling/semantics/prelude.ts
+++ b/src/language/compiling/semantics/prelude.ts
@@ -308,8 +308,6 @@ export const prelude: ObjectNode = makeObjectNode({
   ),
 
   boolean: makeObjectNode({
-    true: 'true',
-    false: 'false',
     is: preludeFunction(
       ['boolean', 'is'],
       {
diff --git a/src/language/parsing/molecule.ts b/src/language/parsing/molecule.ts
index a642356..9119a3c 100644
--- a/src/language/parsing/molecule.ts
+++ b/src/language/parsing/molecule.ts
@@ -90,14 +90,16 @@ const sugaredApply: Parser<PartialMolecule> = parser.map(
     parser.oneOrMore(
       parser.sequence([
         parser.literal('('),
+        optional(omit(whitespace)),
         parser.lazy(() => propertyValue),
+        optional(omit(whitespace)),
         parser.literal(')'),
       ]),
     ),
   ]),
   ([f, multipleArguments]) =>
     multipleArguments.reduce<PartialMolecule>(
-      (expression, [_1, argument, _2]) => ({
+      (expression, [_1, _2, argument, _3, _4]) => ({
         0: '@apply',
         function: expression,
         argument,
diff --git a/src/language/semantics/type-system/subtyping.ts b/src/language/semantics/type-system/subtyping.ts
index bf66e8a..c117516 100644
--- a/src/language/semantics/type-system/subtyping.ts
+++ b/src/language/semantics/type-system/subtyping.ts
@@ -232,12 +232,12 @@ const isNonUnionAssignableToUnion = ({
   if (source.kind === 'opaque') {
     return source.isAssignableTo(target)
   } else {
-    // The strategy for this case is to check whether any of the target's members are
-    // assignable to the source type. However this alone is not sufficient—for example
-    // `{ a: 'a' | 'b' }` should be assignable to `{ a: 'a' } | { a: 'b' }` even though
-    // `{ a: 'a' | 'b' }` is not directly assignable to `{ a: 'a' }` nor `{ a: 'b' }`. To
-    // make things work the target type is first converted into a standard form (e.g.
-    // `{ a: 'a' } | { a: 'b' }` is translated into `{ a: 'a' | 'b' }`.
+    // The strategy for this case is to check whether any of the target's members are assignable to
+    // the source type. However this alone is not sufficient—for example `{ a: 'a' | 'b' }` should
+    // be assignable to `{ a: 'a' } | { a: 'b' }` even though `{ a: 'a' | 'b' }` is not directly
+    // assignable to `{ a: 'a' }` nor `{ a: 'b' }`. To make things work the target type is first
+    // converted into a standard form (e.g. `{ a: 'a' } | { a: 'b' }` is translated into
+    // `{ a: 'a' | 'b' }`.
 
     const preparedTarget = simplifyUnionType(target)
 
@@ -290,7 +290,7 @@ export const simplifyUnionType = (typeToSimplify: UnionType): UnionType => {
   const reducibleSubsets: Map<
     string,
     {
-      readonly keys: string[]
+      readonly keys: readonly string[]
       readonly typesToMerge: Set<ObjectType>
     }
   > = new Map()
@@ -298,12 +298,10 @@ export const simplifyUnionType = (typeToSimplify: UnionType): UnionType => {
     if (typeof type !== 'string' && type.kind === 'object') {
       const keys = Object.keys(type.children)
 
-      // Object types with a single key are always mergeable with other object types
-      // containing the same single key. For example `{ a: 'a' } | { a: 'b' }` can become
-      // `{ a: 'a' | 'b' }`.
-      // TODO: Handle cases where there is more than one key but property types are
-      // compatible. For example `{ a: 'a', b: 'b' } | { a: 'b', b: 'b' }` can become
-      // `{ a: 'a' | 'b', b: 'b' }`.
+      // Object types with a single key are always mergeable with other object types containing the
+      // same single key. For example `{ a: 'a' } | { a: 'b' }` can become `{ a: 'a' | 'b' }`.
+      // TODO: Handle cases where there is more than one key but property types are compatible. For
+      // example `{ a: 'a', b: 'b' } | { a: 'b', b: 'b' }` can become `{ a: 'a' | 'b', b: 'b' }`.
       const fingerprint = keys[0]
       if (keys.length === 1 && fingerprint !== undefined) {
         const objectTypesWithThisFingerprint = reducibleSubsets.get(
@@ -319,6 +317,7 @@ export const simplifyUnionType = (typeToSimplify: UnionType): UnionType => {
 
   const canonicalizedTargetMembers: Set<Atom | Exclude<Type, UnionType>> =
     new Set([...typeToSimplify.members])
+
   // Reduce `reducibleSubsets` by merging all candidate, updating `canonicalizedTargetMembers`.
   // Merge algorithm:
   //  - for each reducible subset of object types: