diff --git a/private/common.rkt b/private/common.rkt
index 4c275da..83bebb2 100644
--- a/private/common.rkt
+++ b/private/common.rkt
@@ -3,9 +3,6 @@
 ;; Common helper functions
 
 (provide
-  expand-expr
-  ;; (-> Syntax Syntax)
-  ;; Call local expand for an expression context with an empty list of stop-ids
 
   quoted-stx-value?
   ;; (-> Any (U #f Syntax))
@@ -15,20 +12,31 @@
 
   define-syntax-class/predicate
   ;; (stx-> Identifier (-> Any Boolean) SyntaxClassDef)
+
+  make-value-property
+  ;; TODO
+
+  make-alias
+  ;; TODO
 )
 
 (require
+  racket/syntax
   syntax/parse
+  syntax/id-table
+  (for-syntax (only-in typed/racket/base let let-syntax #%app))
   (for-template (only-in typed/racket/base quote)))
 
 ;; =============================================================================
 
 (define-syntax-rule (define-syntax-class/predicate id p?)
   (define-syntax-class id
-   #:attributes (expanded)
+   #:attributes (evidence expanded)
    (pattern e
-    #:with e+ (quoted-stx-value? (expand-expr #'e))
-    #:when (p? (syntax-e #'e+))
+    #:with e+ (expand-expr #'e)
+    #:with p+ (p? #'e+)
+    #:when (if (syntax-e #'p+) #t (begin (printf "ERROR we failed iwth ~a\n" (syntax->datum #'e+)) #f)) ;; TODO remove this
+    #:attr evidence #'p+
     #:attr expanded #'e+)))
 
 (define (expand-expr stx)
@@ -41,3 +49,66 @@
      [(quote v)
       (syntax-e #'v)]
      [else #f])))
+
+;; In:
+;; - name : Symbol, like format-spec or vector-length or db-schema
+;; - parser : (Syntax -> Value)
+;;            Syntax is anything, need to filter yourself
+;;            Value is the important type++ data
+;; Out:
+;; - (Syntax -> (Option Syntax)) x3
+;;   1st is recognizer, cooperates with define & let
+;;   2nd is define form
+;;   3rd is let form
+;; - id table
+;; - syntax property key
+;; Put transformers here too? Then the id table never escapes
+(define (make-value-property sym parser)
+  (define key (gensym sym))
+  (define tbl (make-free-id-table))
+  (define f-parse
+    (lambda (stx)
+      (let ([v (syntax-property stx key)])
+        (cond
+         [v                  v]
+         [(identifier? stx)  (free-id-table-ref tbl stx #f)]
+         [else               (parser stx)]))))
+  (define f-define
+    (lambda (stx)
+      (syntax-parse stx
+       [(_ name:id v)
+        #:with v+ (expand-expr #'v)
+        #:when (syntax-e #'v+)
+        #:with m (f-parse #'v+)
+        #:when (syntax-e #'m)
+        (free-id-table-set! #'name (syntax-e #'m))
+        (syntax/loc stx
+          (define name v+))]
+       [_ #f])))
+  (define f-let
+    (lambda (stx)
+      (syntax-parse stx
+       [(_ ([name*:id v*] ...) e* ...)
+        #:with (v+* ...) (map expand-expr (syntax-e #'(v* ...)))
+        #:when (andmap syntax-e (syntax-e #'(v+* ...)))
+        #:with (m* ...) (map f-parse (syntax-e #'(v+* ...)))
+        #:when (andmap syntax-e (syntax-e #'(m* ...)))
+        #:with let-stx (format-id stx "let")
+        #:with let-syntax-stx (format-id stx "let-syntax")
+        (quasisyntax/loc stx
+          (let-stx ([name* v+*] ...)
+            (let-syntax-stx ([name* (make-rename-transformer
+                                  (syntax-property #'name* '#,key 'm* ...))] ...)
+              e* ...)))]
+       [_ #f])))
+  (values
+    key
+    f-parse
+    f-define
+    f-let))
+
+(define ((make-alias id-stx parser) stx)
+  (or (parser stx)
+    (syntax-parse stx
+     [_:id       (quasisyntax/loc stx #,id-stx)]
+     [(_ e* ...) (quasisyntax/loc stx (#,id-stx e* ...))])))