between/c (unlike integer-in) can actually just disappear

when the arguments are = to each other

pkgs/racket-test/tests/racket/contract/flat-contracts.rkt

@@ -177,6 +177,8 @@
   
   (test-flat-contract '(between/c 1 10) 3 11)
   (test-flat-contract '(between/c 1 10) 4 1+1i)
+  (test-flat-contract '(between/c 9 9) 9 10)
+  (test-flat-contract '(between/c 9 9) 9.0 10)
   (test-flat-contract '(<=/c 1) 0 1+1i)
   (test-flat-contract '(</c 1) 0 1+1i)
   (test-flat-contract '(>/c 1) 4 1+1i)

pkgs/racket-test/tests/racket/contract/name.rkt

@@ -183,7 +183,9 @@
   (test-name '(>/c 5) (>/c 5))
   (test-name '(between/c 5 6) (between/c 5 6))
   (test-name '(between/c -inf.0 +inf.0) (between/c -inf.0 +inf.0))
+  (test-name '5 (between/c 5 5))
   (test-name '(integer-in 0 10) (integer-in 0 10))
+  (test-name '(and/c 0 exact?) (integer-in 0 0))
   (test-name '(real-in 1 10) (real-in 1 10))
   (test-name '(between/c 1 10) (between/c 1 10))
   (test-name '(string-len/c 3) (string-len/c 3))

racket/collects/racket/contract/private/misc.rkt

@@ -441,7 +441,9 @@
   (check-two-args 'between/c x y real? real?))
 (define/final-prop (between/c x y)
   (check-between/c x y)
-  (make-between/c-s x y))
+  (if (= x y)
+      (coerce-contract 'between/c x)
+      (make-between/c-s x y)))
 
 (define (make-</c->/c-contract-property name </> -/+ less/greater)
   (build-flat-contract-property

racket/collects/racket/contract/private/opters.rkt

@@ -195,7 +195,9 @@
                                      [that that])
                          (syntax (<= this that))))))
               #:chaperone #t
-              #:name #''(between/c n m))))))]
+              #:name #'(if (= n m)
+                           n
+                           '(between/c n m)))))))]
     [_ (opt/unknown opt/i opt/info stx)]))
 
 (define (raise-opt-between/c-error blame val lo hi)