diff --git a/collects/schelog/schelog.rkt b/collects/schelog/schelog.rkt
index 4d1a5aecf7..f2fce161dc 100644
--- a/collects/schelog/schelog.rkt
+++ b/collects/schelog/schelog.rkt
@@ -121,7 +121,7 @@
          __fk)))))
 
 (define-syntax-parameter !
-  (λ (stx) (raise-syntax-error '! "May only be used inside goal expression." stx)))
+  (λ (stx) (raise-syntax-error '! "May only be used syntactically inside %rel or %cut-delimiter expression." stx)))
 
 (define-syntax %cut-delimiter
   (syntax-rules ()
@@ -157,20 +157,23 @@
   (lambda (fk) fk))
 
 (define-syntax %is
-  (syntax-rules (quote)
+  (syntax-rules ()
     ((%is v e)
      (lambda (__fk)
-       ((%= v (%is (1) e __fk)) __fk)))
-    
-    ((%is (1) (quote x) fk) (quote x))
-    ((%is (1) (x ...) fk)
-     ((%is (1) x fk) ...))
-    ((%is (1) x fk)
+       ((%= v (%is/fk e __fk)) __fk)))))
+(define-syntax %is/fk
+  (syntax-rules (quote)
+    ((%is/fk (quote x) fk) (quote x))
+    ((%is/fk (x ...) fk)
+     ((%is/fk x fk) ...))
+    ((%is/fk x fk)
      (if (and (logic-var? x) (unbound-logic-var? x))
          (fk 'fail) (logic-var-val* x)))))
 
 (define ((make-binary-arithmetic-relation f) x y)
-  (%is #t (f x y)))
+  (%and (%is #t (number? x))
+        (%is #t (number? y))
+        (%is #t (f x y))))
 
 (define %=:= (make-binary-arithmetic-relation =))
 (define %> (make-binary-arithmetic-relation >))
diff --git a/collects/tests/schelog/unit.rkt b/collects/tests/schelog/unit.rkt
new file mode 100644
index 0000000000..802c9d2f33
--- /dev/null
+++ b/collects/tests/schelog/unit.rkt
@@ -0,0 +1,271 @@
+#lang racket
+(require schelog
+         tests/eli-tester)
+
+(test
+ (logic-var? (_))
+ 
+ (%which () (%/= 1 1)) => #f
+ (%which () (%/= 1 2)) => empty
+ (%more) => #f
+ 
+ (%which (x) (%/== x x)) => #f
+ (%which (x y) (%/== x y)) => `((x . _) (y . _))
+ (%more) => #f
+ 
+ (%which () (%/== 1 1)) => #f
+ (%which () (%/== 1 2)) => empty
+ (%more) => #f
+ 
+ (%which () (%< 1 2)) => empty
+ (%more) => #f
+ (%which () (%< 1 1)) => #f
+ (%which () (%< 2 1)) => #f
+ (%which () (%< 'a 2)) => #f
+ (%which () (%< 1 'b)) => #f
+ (%which () (%< 'a 'b)) => #f
+ 
+ (%which () (%<= 1 2)) => empty
+ (%more) => #f
+ (%which () (%<= 1 1)) => empty
+ (%more) => #f
+ (%which () (%<= 2 1)) => #f
+ (%which () (%<= 'a 2)) => #f
+ (%which () (%<= 1 'b)) => #f
+ (%which () (%<= 'a 'b)) => #f
+ 
+ (%which () (%= 1 1)) => empty
+ (%more) => #f
+ (%which () (%= 'a 'a)) => empty
+ (%more) => #f
+ (%which () (%= (cons 1 2) (cons 1 2))) => empty
+ (%more) => #f
+ (%which () (%= (vector 1 2) (vector 1 2))) => empty
+ (%more) => #f
+ (%which (x) (%= x 1)) => `((x . 1))
+ (%more) => #f
+ (%which (x) (%= (cons x 2) (cons 1 2))) => `((x . 1))
+ (%more) => #f
+ (%which (x) (%= (vector x 2) (vector 1 2))) => `((x . 1))
+ (%more) => #f
+ (%which (x) (%and (%= x 1) (%= x 2))) => #f
+ (%which () (%= 1 2)) => #f
+ 
+ (%which () (%=/= 1 1)) => #f
+ (%which () (%=/= 'a 'a)) => #f
+ (%which () (%=/= 1 2)) => empty
+ (%more) => #f
+ 
+ (%which () (%=:= 1 1)) => empty
+ (%more) => #f
+ (%which () (%=:= 'a 'a)) => #f
+ (%which () (%=:= 1 2)) => #f
+
+ (%which () (%== 1 1)) => empty
+ (%more) => #f
+ (%which (x) (%== x x)) => `((x . _))
+ (%more) => #f
+ (%which (x) (%== (cons 1 x) (cons 1 x))) => `((x . _))
+ (%more) => #f
+ ; XXX This answer seems wrong
+ (%which (x) (%and (%= x 1) (%== x 1))) => `((x . 1))
+ (%more) => #f
+ ; XXX This answer seems wrong
+ (%which (x y) (%and (%= x 1) (%= y 1) (%== x y))) => `((x . 1) (y . 1))
+ (%more) => #f
+ (%which (x y) (%== x y)) => #f
+ (%which (x y) (%== (cons 1 x) (cons y 2))) => #f
+ 
+ (%which () (%> 2 1)) => empty
+ (%more) => #f
+ (%which () (%> 1 1)) => #f
+ (%which () (%> 1 2)) => #f
+ (%which () (%> 'a 2)) => #f
+ (%which () (%> 1 'b)) => #f
+ (%which () (%> 'a 'b)) => #f
+ 
+ (%which () (%>= 2 1)) => empty
+ (%more) => #f
+ (%which () (%>= 1 1)) => empty
+ (%more) => #f
+ (%which () (%>= 1 2)) => #f
+ (%which () (%>= 'a 2)) => #f
+ (%which () (%>= 1 'b)) => #f
+ (%which () (%>= 'a 'b)) => #f 
+ 
+ (%which () (%and %true %true)) => empty
+ (%more) => #f
+ (%which () (%and %fail %true)) => #f
+ (%more) => #f
+ 
+ (%which () (%append empty empty empty)) => empty
+ (%more) => #f
+ (%which () (%append (list 1) empty (list 1))) => empty
+ (%more) => #f
+ (%which () (%append empty (list 2) (list 2))) => empty
+ (%more) => #f
+ (%which () (%append (list 1) (list 2) (list 1 2))) => empty
+ (%more) => #f
+ 
+ (let ([rel %empty-rel])
+   (test (%which (y) (rel 'x y)) => #f
+         (%assert rel () [('x 1)])
+         (%which (y) (rel 'x y)) => `([y . 1])
+         (%more) => #f
+         (%assert-a rel () [('x 2)])
+         (%which (y) (rel 'x y)) => `([y . 2])
+         (%more) => `([y . 1])
+         (%more) => #f
+         (%assert rel () [('x 3)])
+         (%which (y) (rel 'x y)) => `([y . 2])
+         (%more) => `([y . 1])
+         (%more) => `([y . 3])
+         (%more) => #f))
+         
+ (%which (y) (%let (x) (%bag-of x (%or (%= x 1) (%= x 1) (%= x 2)) y))) => `([y . (1 1 2)])
+ (%more) => #f
+ ; XXX I don't know a program that would get these outputs
+ ;(%which (y) (%let (x) (%bag-of x XXX y))) => `([y . ()])
+ (%more) => #f
+ (%which (y) (%let (x) (%bag-of-1 x (%or (%= x 1) (%= x 1) (%= x 2)) y))) => `([y . (1 1 2)])
+ (%more) => #f
+ ; XXX I don't know a program that would get these outputs
+ ;(%which (y) (%let (x) (%bag-of-1 x XXX y))) => #f
+ 
+ (%which () (%compound (cons 1 1))) => empty
+ (%more) => #f
+ (%which () (%compound (vector 1 1))) => empty
+ (%more) => #f
+ (%which () (%let (x) (%and (%= x (cons 1 1)) (%compound x)))) => empty
+ (%more) => #f
+ (%which () (%compound 1)) => #f 
+ (%which () (%compound "1")) => #f 
+ (%which () (%compound '1)) => #f 
+ (%which () (%compound empty)) => #f 
+ 
+ (%which () (%constant (cons 1 1))) => #f
+ (%which () (%constant (vector 1 1))) => #f
+ (%which () (%let (x) (%and (%= x 1) (%constant x)))) => empty
+ (%more) => #f
+ (%which () (%constant 1)) => empty
+ (%more) => #f
+ (%which () (%constant "1")) => empty
+ (%more) => #f
+ (%which () (%constant '1)) => empty
+ (%more) => #f
+ (%which () (%constant empty)) => empty
+ (%more) => #f
+ 
+ ; XXX %copy
+ 
+ ! =error> "syntactically"
+ 
+ (%which () (%cut-delimiter %true)) => empty
+ (%more) => #f
+ (%which () (%cut-delimiter !)) => empty
+ (%more) => #f
+ (%which () (%cut-delimiter %fail)) => #f
+ (%which () (%or %true %true)) => empty
+ (%more) => empty
+ (%more) => #f
+ (%which () (%cut-delimiter (%or (%and ! %true) %true))) => empty
+ (%more) => #f
+ 
+ (%which () (%empty-rel 1 1)) => #f
+ 
+ (%which () %fail) => #f
+ 
+ ; XXX %free-vars
+ 
+ ; XXX %freeze
+ 
+ (%which () (%if-then-else %true %true %true)) => empty
+ (%more) => #f
+ (%which () (%if-then-else %true %fail %true)) => #f
+ (%which () (%if-then-else %fail %true %true)) => empty
+ (%more) => #f
+ 
+ (%which (x) (%is x (* 6 7))) => `([x . 42])
+ (%more) => #f
+ (%which (x) (%let (y) (%and (%= y 7) (%is x (* 6 y))))) => `([x . 42])
+ (%more) => #f
+ 
+ (%which () (%let (x) (%= x x))) => empty
+ (%more) => #f
+ 
+ ; XXX %melt
+ 
+ ; XXX %melt-ne
+ 
+ (%which () (%member 3 (list 1 2 3))) => empty
+ (%more) => #f
+ (%which () (%member 3 (list 1 2 3 3))) => empty
+ (%more) => empty
+ (%more) => #f
+ (%which () (%member 3 (list 1 2))) => #f
+ 
+ (%which () (%let (x) (%nonvar x))) => #f
+ (%which () (%let (x) (%nonvar (cons 1 x)))) => #f
+ (%which () (%let (x) (%nonvar (vector x)))) => #f
+ (%which () (%let (x) (%nonvar 1))) => empty
+ (%more) => #f
+ (%which () (%let (x) (%and (%= x 1) (%nonvar x)))) => empty
+ (%more) => #f
+ 
+ (%which () (%not %true)) => #f
+ (%which () (%not %fail)) => empty
+ (%more) => #f
+ 
+ (%which () (%or %true %true)) => empty
+ (%more) => empty
+ (%more) => #f
+ (%which () (%or %true %fail %true)) => empty
+ (%more) => empty
+ (%more) => #f
+ 
+ (let ([rel (%rel () [(1)] [(2) %fail])])
+   (test (%which () (rel 1)) => empty
+         (%more) => #f
+         (%which () (rel 2)) => #f))
+ (let ([rel (%rel () [(1) !] [(1) (%repeat)])])
+   (test (%which () (rel 1)) => empty
+         (%more) => #f))
+         
+ (local [(define (many-%more n)
+           (if (zero? n)
+               empty
+               (and (%more)
+                    (many-%more (sub1 n)))))]
+   (test (%which () (%repeat)) => empty
+         (many-%more (random 50)) => empty))
+ 
+ (parameterize ([use-occurs-check? #f])
+   (%which () (%let (x) (%= x (cons 1 x))))) 
+ => empty
+ (parameterize ([use-occurs-check? #t])
+   (%which () (%let (x) (%= x (cons 1 x)))))
+ => #f
+
+ (%which (y) (%let (x) (%set-of x (%or (%= x 1) (%= x 1) (%= x 2)) y))) => `([y . (1 2)])
+ (%more) => #f
+ ; XXX I don't know a program that would get these outputs
+ ;(%which (y) (%let (x) (%set-of x XXX y))) => `([y . ()])
+ (%more) => #f
+ (%which (y) (%let (x) (%set-of-1 x (%or (%= x 1) (%= x 1) (%= x 2)) y))) => `([y . (1 2)])
+ (%more) => #f
+ ; XXX I don't know a program that would get these outputs
+ ;(%which (y) (%let (x) (%set-of-1 x XXX y))) => #f
+ 
+ (%which () %true) => empty
+ (%more) => #f
+ 
+ (%which () (%let (x) (%var x))) => empty
+ (%more) => #f
+ (%which () (%let (x) (%var (cons 1 x)))) => empty
+ (%more) => #f
+ (%which () (%let (x) (%var (vector x)))) => empty
+ (%more) => #f
+ (%which () (%let (x) (%var 1))) => #f
+ (%which () (%let (x) (%and (%= x 1) (%var x)))) => #f
+ 
+ )
\ No newline at end of file