diff --git a/2016/day07.rkt b/2016/day07.rkt
index 78c66e9..0448975 100644
--- a/2016/day07.rkt
+++ b/2016/day07.rkt
@@ -11,14 +11,49 @@
 (provide (rename-out [mb #%module-begin]))
 (define-macro (mb . IPS)
   #'(#%module-begin
-     (length (filter supports-tls? (list . IPS)))
-     (map supports-tls? (list . IPS))))
+     (define ips (list . IPS))
+     (displayln (format "part a: ~a" (length (filter supports-tls? ips))))
+     (displayln (format "part b: ~a" (length (filter supports-ssl? ips))))))
 
-(define (supports-tls? x)
+(define bracketed-pattern #rx"\\[.*?\\]")
+
+(define (bracketed-parts str)
+  (regexp-match* bracketed-pattern str))
+
+(define (unbracketed-parts str)
+  (string-split str bracketed-pattern))
+
+(define (has-abba? str)
+  (for*/or ([idx (in-range (string-length str))]
+            [substr (in-list (regexp-match* #px"^\\w\\w\\w\\w" str idx))]
+            #:when substr)
+    (define cs (string->list substr))
+    (and
+     (char=? (first cs) (fourth cs))
+     (char=? (second cs) (third cs))
+     (not (char=? (first cs) (second cs))))))
+
+(define (supports-tls? str)
   (and
-   (let ([maybe-abbas (regexp-match* #px"(\\w)(\\w)\\2\\1" x)])
-     (ormap (λ(ma)
-              (not (equal? (substring ma 0 1) (substring ma 1 2)))) maybe-abbas))
-   (let ([maybe-bad-abbas (regexp-match* #px"\\[.*((\\w)(\\w)\\3\\2).*\\]" x #:match-select cadr)])
-     (andmap (λ(ma)
-               (equal? (substring ma 0 1) (substring ma 1 2))) maybe-bad-abbas))))
+   (ormap has-abba? (unbracketed-parts str))
+   (andmap (negate has-abba?) (bracketed-parts str))))
+
+(define (find-abas str)
+  (for*/list ([idx (in-range (string-length str))]
+              [substr (in-list (regexp-match* #px"^\\w\\w\\w" str idx))]
+              [cs (in-value (string->list substr))]
+              #:when (and
+                      substr
+                      (char=? (first cs) (third cs))
+                      (not (char=? (first cs) (second cs)))))
+    substr))
+
+(define (aba->bab aba) (format "~a~a~a" (substring aba 1 2)
+                               (substring aba 0 1)
+                               (substring aba 1 2)))
+
+(define (supports-ssl? str)
+  (define abas (append-map find-abas (unbracketed-parts str)))
+  (for*/or ([bab (in-list (map aba->bab abas))]
+            [str (in-list (bracketed-parts str))])
+    (regexp-match bab str)))