diff --git a/sketching/september_2025/adder/adder.dm b/sketching/september_2025/adder/adder.dm
new file mode 100644
index 0000000..3ce2ca7
--- /dev/null
+++ b/sketching/september_2025/adder/adder.dm
@@ -0,0 +1,5 @@
+use math::add
+
+fn main()
+    println add(1, 2) // 3
+end
\ No newline at end of file
diff --git a/sketching/september_2025/adder/math/add.dm b/sketching/september_2025/adder/math/add.dm
new file mode 100644
index 0000000..94e44a9
--- /dev/null
+++ b/sketching/september_2025/adder/math/add.dm
@@ -0,0 +1,3 @@
+mod math
+
+pub fn add(a: Int, b: Int) = a + b
diff --git a/src/parser/ast.schema.yaml b/src/parser/ast.schema.yaml
index fa2f366..695f091 100644
--- a/src/parser/ast.schema.yaml
+++ b/src/parser/ast.schema.yaml
@@ -78,12 +78,14 @@ $defs:
     properties:
       rule:
         type: string
+        description: The type to build, in Pascal case.
+      optional:
+        type: boolean
+        description: If true, this child will be stored as an Option.
       build:
         oneOf:
           - type: string
           - $ref: "#/$defs/SingleChildBuildDefinition"
-    required:
-      - rule
   SingleChildBuildDefinition:
     type: object
     additionalProperties: false
diff --git a/src/parser/ast.yaml b/src/parser/ast.yaml
index 694b428..5d34c8e 100644
--- a/src/parser/ast.yaml
+++ b/src/parser/ast.yaml
@@ -1,19 +1,21 @@
 # $schema: ./ast.schema.yaml
+# Top-level constructs
 CompilationUnit:
   children:
-    - namespace
+    - parent_mod
     - use_statements:
         rule: UseStatement
         vec: true
     - module_level_declarations:
         rule: ModuleLevelDeclaration
-Namespace:
+        vec: true
+ParentMod:
   children:
-    - ns_kw:
-        rule: Ns
+    - mod_kw:
+        rule: Mod
         skip: true
     - fqn:
-        rule: Fqn
+        rule: FullyQualifiedName
 UseStatement:
   children:
     - use_kw:
@@ -24,17 +26,49 @@ UseStatement:
         vec: true
     - suffix:
         rule: UseStatementSuffix
+UseStatementPrefix:
+  children:
+    - identifier
+UseStatementSuffix:
+  rules:
+    - Identifier
+    - rule: Star
+      build: UseStatementStarSuffix
+    - UseList
+UseList:
+  children:
+    - identifiers:
+        rule: Identifier
+        vec: true
+
+# Level declarations
 ModuleLevelDeclaration:
   rules:
-    - rule: Module
-      build: ModuleDeclaration
-    - rule: Interface
-      build: InterfaceDeclaration
-    - rule: Class
-      build: ClassDeclaration
-    - FunctionDefinition
+    - Module
+    - Interface
+    - Class
+    - Function
     - PlatformFunction
-ModuleDeclaration:
+InterfaceLevelDeclaration:
+  rules:
+    - CompanionModule
+    - Interface
+    - Class
+    - InterfaceFunction
+    - InterfaceDefaultFunction
+    - InterfaceOperatorFunction
+    - InterfaceDefaultOperatorFunction
+ClassLevelDeclaration:
+  children:
+    - CompanionModule
+    - Interface
+    - Class
+    - Function
+    - OperatorFunction
+    - PlatformFunction
+
+# Main organizational constructs
+Module:
   children:
     - is_public:
         rule: Pub
@@ -49,7 +83,45 @@ ModuleDeclaration:
     - declarations:
         rule: ModuleLevelDeclaration
         vec: true
-ClassDeclaration:
+    - end_kw:
+        rule: End
+        skip: true
+CompanionModule:
+  children:
+    - companion_kw:
+        rule: Companion
+        skip: true
+    - mod_kw:
+        rule: Mod
+        skip: true
+    - declarations:
+        rule: ModuleLevelDeclaration
+        vec: true
+    - end_kw:
+        rule: End
+        skip: true
+Interface:
+  children:
+    - is_public:
+        rule: Pub
+        build:
+          type: boolean
+          on: rule_present
+    - int_kw:
+        rule: IntKw
+        skip: true
+    - identifier
+    - generic_parameters:
+        optional: true
+    - implements_list:
+        optional: true
+    - declarations:
+        rule: InterfaceLevelDeclaration
+        vec: true
+    - end_kw:
+        rule: End
+        skip: true
+Class:
   children:
     - is_public:
         rule: Pub
@@ -60,13 +132,18 @@ ClassDeclaration:
         rule: ClassKw
         skip: true
     - identifier
-    - generic_parameters
-    - class_constructor
-    - implements_list
+    - generic_parameters:
+        optional: true
+    - class_constructor:
+        optional: true
+    - implements_list:
+        optional: true
     - class_level_declarations:
         rule: ClassLevelDeclaration
         vec: true
-FunctionDeclaration:
+
+# Function constructs
+Function:
   children:
     - is_public:
         rule: Pub
diff --git a/src/parser/deimos.pest b/src/parser/deimos.pest
index bbcc876..c8ead30 100644
--- a/src/parser/deimos.pest
+++ b/src/parser/deimos.pest
@@ -30,6 +30,8 @@ Alias = { "alias" }
 True = { "true" }
 False = { "false" }
 Use = { "use" }
+End = { "end" }
+Companion = { "comp" }
 
 // Keywords: primitive types
 Byte = { "Byte" }
@@ -322,22 +324,31 @@ RefList = {
 
 CompilationUnit = {
       SOI
-    ~ ( Namespace ~ Semicolon )?
-    ~ ( UseStatement ~ Semicolon )*
-    ~ ModuleLevelDeclaration*
+    ~ ParentMod?
+    ~ ( UseStatement | ModuleLevelDeclaration )*
     ~ EOI
 }
 
-Namespace = {
-      Ns
+ParentMod = {
+      Mod
     ~ FullyQualifiedName
 }
 
 UseStatement = {
       Use
-    ~ Identifier
-    ~ ( "::" ~ Identifier )*
-    ~ ( "::" ~ ( Star | UseList ) )?
+    ~ UseStatementPrefix*
+    ~ UseStatementSuffix
+}
+
+UseStatementPrefix = {
+      Identifier
+    ~ "::"
+}
+
+UseStatementSuffix = {
+      Identifier
+    | Star
+    | UseList
 }
 
 UseList = {
@@ -353,12 +364,12 @@ ModuleLevelDeclaration = {
       Module
     | Interface
     | Class
-    | FunctionDefinition
+    | Function
     | PlatformFunction
 }
 
 InterfaceLevelDeclaration = {
-      Module
+      CompanionModule
     | Interface
     | Class
     | InterfaceFunction
@@ -368,14 +379,12 @@ InterfaceLevelDeclaration = {
 }
 
 ClassLevelDeclaration = {
-      Module
+      CompanionModule
     | Interface
     | Class
-    | FunctionDefinition
-    | OperatorFunctionDefinition
+    | Function
+    | OperatorFunction
     | PlatformFunction
-    | Property
-    | Field
 }
 
 // Main organizational constructs
@@ -384,7 +393,15 @@ Module = {
       Pub?
     ~ Mod
     ~ Identifier
-    ~ "{" ~ ModuleLevelDeclaration* ~ "}"
+    ~ ModuleLevelDeclaration*
+    ~ End
+}
+
+CompanionModule = {
+      Companion
+    ~ Mod
+    ~ ModuleLevelDeclaration*
+    ~ End
 }
 
 Interface = {
@@ -393,7 +410,8 @@ Interface = {
     ~ Identifier
     ~ GenericParameters?
     ~ ImplementsList?
-    ~ ( "{" ~ InterfaceLevelDeclaration* ~ "}" )?
+    ~ InterfaceLevelDeclaration*
+    ~ End
 }
 
 Class = {
@@ -403,7 +421,8 @@ Class = {
     ~ GenericParameters?
     ~ ClassConstructor?
     ~ ImplementsList?
-    ~ ( "{" ~ ClassLevelDeclaration* ~ "}" )?
+    ~ ClassLevelDeclaration*
+    ~ End
 }
 
 // Function constructs