diff --git a/tapl/exist.rkt b/tapl/exist.rkt
index e3c51eb..8d0d6a2 100644
--- a/tapl/exist.rkt
+++ b/tapl/exist.rkt
@@ -1,5 +1,4 @@
-#lang racket/base
-(require "typecheck.rkt")
+#lang s-exp "typecheck.rkt"
 (require (except-in "stlc+reco+var.rkt" #%app λ let)
          (prefix-in stlc: (only-in "stlc+reco+var.rkt" #%app λ let))
          (only-in "stlc+rec-iso.rkt")) ; to get current-type=?
diff --git a/tapl/ext-stlc.rkt b/tapl/ext-stlc.rkt
index 8ef4986..ddd0888 100644
--- a/tapl/ext-stlc.rkt
+++ b/tapl/ext-stlc.rkt
@@ -1,5 +1,4 @@
-#lang racket/base
-(require "typecheck.rkt")
+#lang s-exp "typecheck.rkt"
 ;; prefix-in an identifier if:
 ;; - it will be extended, eg #%datum
 ;; - want to use racket's version in implemetation (this) file, eg #%app
diff --git a/tapl/fomega.rkt b/tapl/fomega.rkt
index b2d0a08..b814f90 100644
--- a/tapl/fomega.rkt
+++ b/tapl/fomega.rkt
@@ -1,5 +1,4 @@
-#lang racket/base
-(require "typecheck.rkt")
+#lang s-exp "typecheck.rkt"
 (require (except-in "sysf.rkt" #%app λ #%datum Λ inst ∀)
          (rename-in (prefix-in sysf: (only-in "sysf.rkt" #%app λ ∀ ~∀))
                     [sysf:~∀ ~sysf:∀])
diff --git a/tapl/fomega2.rkt b/tapl/fomega2.rkt
index ff0b3f5..6552499 100644
--- a/tapl/fomega2.rkt
+++ b/tapl/fomega2.rkt
@@ -1,5 +1,4 @@
-#lang racket/base
-(require "typecheck.rkt")
+#lang s-exp "typecheck.rkt"
 (require (except-in "sysf.rkt" #%app λ #%datum Λ inst ∀)
          (rename-in (prefix-in sysf: (only-in "sysf.rkt" #%app λ ∀ ~∀))
                     [sysf:~∀ ~sysf:∀])
diff --git a/tapl/fsub.rkt b/tapl/fsub.rkt
index 995b8ac..5a70d2a 100644
--- a/tapl/fsub.rkt
+++ b/tapl/fsub.rkt
@@ -1,5 +1,4 @@
-#lang racket/base
-(require "typecheck.rkt")
+#lang s-exp "typecheck.rkt"
 (require (except-in "stlc+reco+sub.rkt" #%app λ +)
          (prefix-in stlc: (only-in "stlc+reco+sub.rkt" #%app λ))
          (only-in "sysf.rkt" ∀?)
diff --git a/tapl/stlc+box.rkt b/tapl/stlc+box.rkt
index a84512d..46dc8fb 100644
--- a/tapl/stlc+box.rkt
+++ b/tapl/stlc+box.rkt
@@ -1,5 +1,4 @@
-#lang racket/base
-(require "typecheck.rkt")
+#lang s-exp "typecheck.rkt"
 (require (prefix-in stlc: (only-in "stlc+cons.rkt" #%app))
          (except-in "stlc+cons.rkt" #%app))
 (provide (rename-out [stlc:#%app #%app]))
diff --git a/tapl/stlc+cons.rkt b/tapl/stlc+cons.rkt
index 39458c3..54fe74d 100644
--- a/tapl/stlc+cons.rkt
+++ b/tapl/stlc+cons.rkt
@@ -1,5 +1,4 @@
-#lang racket/base
-(require "typecheck.rkt")
+#lang s-exp "typecheck.rkt"
 (require (prefix-in stlc: (only-in "stlc+reco+var.rkt" #%app))
          (except-in "stlc+reco+var.rkt" #%app))
 (provide (rename-out [stlc:#%app #%app] [cons/tc cons]))
diff --git a/tapl/stlc+lit.rkt b/tapl/stlc+lit.rkt
index 6041fa4..d574e4f 100644
--- a/tapl/stlc+lit.rkt
+++ b/tapl/stlc+lit.rkt
@@ -1,5 +1,4 @@
-#lang racket/base
-(require "typecheck.rkt")
+#lang s-exp "typecheck.rkt"
 ;(extends "stlc.rkt" #:impl-uses (→))
 (require (except-in "stlc.rkt" #%app)
          (prefix-in stlc: (only-in "stlc.rkt" #%app)))
diff --git a/tapl/stlc+rec-iso.rkt b/tapl/stlc+rec-iso.rkt
index c32717e..2ba483c 100644
--- a/tapl/stlc+rec-iso.rkt
+++ b/tapl/stlc+rec-iso.rkt
@@ -1,5 +1,4 @@
-#lang racket/base
-(require "typecheck.rkt")
+#lang s-exp "typecheck.rkt"
 (require (except-in "stlc+tup.rkt" #%app λ) ; import tuples, not records
          (prefix-in stlc: (only-in "stlc+tup.rkt" #%app λ))
          (only-in "stlc+reco+var.rkt" ∨ var case define-type-alias define)) ; and variants
diff --git a/tapl/stlc+reco+sub.rkt b/tapl/stlc+reco+sub.rkt
index 9f52ed3..9aa79cd 100644
--- a/tapl/stlc+reco+sub.rkt
+++ b/tapl/stlc+reco+sub.rkt
@@ -1,5 +1,4 @@
-#lang racket/base
-(require "typecheck.rkt")
+#lang s-exp "typecheck.rkt"
 ;;use type=? and eval-type from stlc+reco+var.rkt, not stlc+sub.rkt
 ;; but extend sub? from stlc+sub.rkt
 (require (except-in "stlc+sub.rkt" #%app #%datum)
diff --git a/tapl/stlc+reco+var.rkt b/tapl/stlc+reco+var.rkt
index 5050cc5..8415d3c 100644
--- a/tapl/stlc+reco+var.rkt
+++ b/tapl/stlc+reco+var.rkt
@@ -1,5 +1,4 @@
-#lang racket/base
-(require "typecheck.rkt")
+#lang s-exp "typecheck.rkt"
 (require (only-in racket/bool symbol=?))
 (require (prefix-in stlc: (only-in "stlc+tup.rkt" #%app begin let × ×?))
          (except-in "stlc+tup.rkt" #%app begin tup proj let ×)
@@ -40,6 +39,15 @@
     [(_ alias:id τ:type)
      #'(define-syntax alias (syntax-parser [x:id #'τ.norm]))]))
 
+(define-syntax (define/tc stx)
+  (syntax-parse stx
+    [(_ x:id e)
+     #:with (e- τ) (infer+erase #'e)
+     #:with y (generate-temporary)
+     #'(begin
+         (define-syntax x (make-rename-transformer (⊢ y : τ)))
+         (define y e-))]))
+
 ; re-define tuples as records
 ; dont use define-type-constructor because I want the : literal syntax
 (define-syntax ×
@@ -138,12 +146,3 @@
      (⊢ (let ([l_e (car e-)])
           (cond [(symbol=? l_e 'l) (let ([x- (cadr e-)]) e_l-)] ...))
         : #,(stx-car #'(τ_el ...)))]))
-
-(define-syntax (define/tc stx)
-  (syntax-parse stx
-    [(_ x:id e)
-     #:with (e- τ) (infer+erase #'e)
-     #:with y (generate-temporary)
-     #'(begin
-         (define-syntax x (make-rename-transformer (⊢ y : τ)))
-         (define y e-))]))
\ No newline at end of file
diff --git a/tapl/stlc+sub.rkt b/tapl/stlc+sub.rkt
index a457874..620bdd7 100644
--- a/tapl/stlc+sub.rkt
+++ b/tapl/stlc+sub.rkt
@@ -1,5 +1,4 @@
-#lang racket/base
-(require "typecheck.rkt")
+#lang s-exp "typecheck.rkt"
 (require (except-in "stlc+lit.rkt" #%datum + #%app)
          (prefix-in stlc: (only-in "stlc+lit.rkt" #%app #%datum)))
 (provide (rename-out [stlc:#%app #%app] [datum/tc #%datum]))
diff --git a/tapl/stlc+tup.rkt b/tapl/stlc+tup.rkt
index 4785419..2693cb7 100644
--- a/tapl/stlc+tup.rkt
+++ b/tapl/stlc+tup.rkt
@@ -1,5 +1,4 @@
-#lang racket/base
-(require "typecheck.rkt")
+#lang s-exp "typecheck.rkt"
 (require (prefix-in stlc: (only-in "ext-stlc.rkt" #%app))
          (except-in "ext-stlc.rkt" #%app))
 (provide (rename-out [stlc:#%app #%app])
diff --git a/tapl/stlc.rkt b/tapl/stlc.rkt
index bed5fe7..4312c1c 100644
--- a/tapl/stlc.rkt
+++ b/tapl/stlc.rkt
@@ -1,5 +1,4 @@
-#lang racket/base
-(require "typecheck.rkt")
+#lang s-exp "typecheck.rkt"
 (provide (rename-out [λ/tc λ] [app/tc #%app]))
 (provide (for-syntax current-type=? types=?))
 (provide #%module-begin #%top-interaction #%top require) ; useful racket forms
diff --git a/tapl/sysf.rkt b/tapl/sysf.rkt
index 4ce13a9..ab86a99 100644
--- a/tapl/sysf.rkt
+++ b/tapl/sysf.rkt
@@ -1,5 +1,4 @@
-#lang racket/base
-(require "typecheck.rkt")
+#lang s-exp "typecheck.rkt"
 (require (except-in "stlc+lit.rkt" #%app λ)
          (prefix-in stlc: (only-in "stlc+lit.rkt" #%app λ))
          (only-in "stlc+rec-iso.rkt")) ; want type=? from here
diff --git a/tapl/typecheck.rkt b/tapl/typecheck.rkt
index bea2c16..4a940dc 100644
--- a/tapl/typecheck.rkt
+++ b/tapl/typecheck.rkt
@@ -7,7 +7,8 @@
   (for-meta 2 racket/base syntax/parse racket/syntax syntax/stx "stx-utils.rkt")
   (for-meta 3 racket/base syntax/parse racket/syntax)
   racket/provide)
-(provide 
+(provide
+ (all-from-out racket/base)
  (for-syntax (all-defined-out)) (all-defined-out)
  (for-syntax
   (all-from-out racket syntax/parse racket/syntax syntax/stx "stx-utils.rkt"))