diff --git a/rosetta-test-py/sendmail-python-emails.py b/rosetta-test-py/sendmail-python-emails.py
index 3b0421c..7719178 100644
--- a/rosetta-test-py/sendmail-python-emails.py
+++ b/rosetta-test-py/sendmail-python-emails.py
@@ -121,7 +121,7 @@ def sendmail_connected(env, backend):
 #
 
 @sendmail_suite.placeholder("sendmail-send-message-full")
-def sendmail_send_message(env, sender:SMTPBackend, message, sender_address, recipient_addresses, cc_addresses, bcc_addresses, custom_headers, message_options, recipients_options):
+def sendmail_send_message(env, sender:SMTPBackend, message, sender_address, recipient_addresses, cc_addresses, bcc_addresses, custom_headers, attachments, message_options, recipients_options):
     try:
         message = emails.Message(text=message,
                                  subject="Test",
@@ -130,6 +130,23 @@ def sendmail_send_message(env, sender:SMTPBackend, message, sender_address, reci
                                  cc=cc_addresses,
                                  bcc=bcc_addresses,
                                  headers=custom_headers,)
+        for attachment in attachments:
+            message_properties = {
+                "content_disposition": attachment["content-disposition"],
+            }            
+            
+            if "file-name" in attachment:
+                message_properties["filename"] = attachment["file-name"]
+            
+            read_mode = "r"
+            if attachment["data"].endswith(".png"):
+                read_mode = "rb"    
+            message_properties["data"] = open(rosetta.fixture_path('sendmail-fixtures/' + attachment["data"]), read_mode)
+            
+            if "content-type" in attachment:
+                message_properties["content_type"] = attachment["content-type"]
+            
+            message.attach(**message_properties)
         return [message.send(smtp=sender,smtp_mail_options=message_options, smtp_rcpt_options=recipients_options)]
     except Exception as e:
         return [e]     
@@ -154,6 +171,9 @@ def sendmail_error(env, result: SMTPResponse):
 # python-emails does mitigation for addresses but detection for other fields
 
 sendmail_suite.run(
+    exclude=(
+        # python-emails does not support attachments without a name
+        "test_attachment_without_a_name",),
     exclude_capabilities=(
         "root.connection.lazy-connection", # TODO: python-emails does not handle failed auth correctly
         "root.connection.eager-connection",
diff --git a/rosetta-test-py/sendmail-redmail.py b/rosetta-test-py/sendmail-redmail.py
index 38917da..2aeb1a9 100644
--- a/rosetta-test-py/sendmail-redmail.py
+++ b/rosetta-test-py/sendmail-redmail.py
@@ -2,6 +2,7 @@
 import socket as socketlib
 import ssl
 from redmail import EmailSender
+import pathlib
 import smtplib
 
 sendmail_suite = rosetta.suite("rosetta-test-suites/sendmail.ros")
@@ -131,15 +132,20 @@ def sendmail_connected(env, sender: EmailSender):
 #
 
 @sendmail_suite.placeholder("sendmail-send-message-full")
-def sendmail_send_message(env, sender: EmailSender, message, sender_address, recipient_addresses, cc_addresses, bcc_addresses, custom_headers, message_options, recipients_options):
+def sendmail_send_message(env, sender: EmailSender, message, sender_address, recipient_addresses, cc_addresses, bcc_addresses, custom_headers, attachments, message_options, recipients_options):
     try:
+        redmail_attachments = {
+            attachment["file-name"]: pathlib.Path(rosetta.fixture_path('sendmail-fixtures/' + attachment["data"])) 
+                for attachment in attachments 
+                if attachment["content-disposition"] == "attachment"}  
         sender.send(sender=sender_address,
                        receivers=recipient_addresses,
                        cc=cc_addresses,
                        bcc=bcc_addresses,  
                        headers=custom_headers,
                        subject="test",
-                       text=message)
+                       text=message,
+                       attachments=redmail_attachments)
     except Exception as e:
         return [e]
     return [True] # EmailSender.send does not return anything related to the sending
@@ -162,8 +168,20 @@ def sendmail_error(env, result):
 # Running
 #
 
+#sendmail_suite.run(only=("test_basic_image_attachment",))
+
 sendmail_suite.run(
     exclude=(
+        # redmail does not support inline disposition
+        "test_text_attachment_with_inline_disposition", 
+        "test_image_attachment_with_inline_disposition",
+        
+        # redmail does not support attachments without a filename
+        "test_attachment_without_a_name",
+        
+        # redmail does not support multiple attachments with the same name
+        "test_multiple_attachments_with_same_name",
+        
         "test_CRLF_detection_in_send-message_recipient", 
         "test_CRLF_mitigation_in_send-message_sender",
         "test_Connect_with_invalid_credentials"), # TODO redmail leaks sockets when credentials are invalid
diff --git a/rosetta-test-suites/sendmail-fixtures/info.txt b/rosetta-test-suites/sendmail-fixtures/info.txt
new file mode 100644
index 0000000..de24153
--- /dev/null
+++ b/rosetta-test-suites/sendmail-fixtures/info.txt
@@ -0,0 +1 @@
+content of info file
\ No newline at end of file
diff --git a/rosetta-test-suites/sendmail-fixtures/test.png b/rosetta-test-suites/sendmail-fixtures/test.png
new file mode 100644
index 0000000..dec35f9
Binary files /dev/null and b/rosetta-test-suites/sendmail-fixtures/test.png differ
diff --git a/rosetta-test-suites/sendmail.ros b/rosetta-test-suites/sendmail.ros
index dfe39b1..bdda5e5 100644
--- a/rosetta-test-suites/sendmail.ros
+++ b/rosetta-test-suites/sendmail.ros
@@ -5,11 +5,10 @@
     ; indepdenent of whether this is done with an API from the tested library directly or by using 
     ; another library, e.g. a MIME library from the standard library.
     (sources 
-		'("CPython SMTP tests" "Python Foundation" "https://github.com/python/cpython/blob/9ba2a4638d7b620c939face7642b2f53a9fadc4b/Lib/test/test_smtplib.py")
-        '("Ruby net-smtp tests" "MRI maintainers" "https://github.com/ruby/net-smtp/blob/master/test/net/smtp/test_smtp.rb")
+		'("Ruby mail gem spec" "Mikel Lindsaar" "https://github.com/mikel/mail") 
         '("SMTP RFC 2821" "IETF" "https://tools.ietf.org/html/rfc2821")
         '("SMTP RFC 5321" "IETF" "https://tools.ietf.org/html/rfc5321")
-        '("SMTP RFC 4954" "IETF" "https://tools.ietf.org/html/rfc4954"))
+        '("RFC 2183 - Content-Disposition" "IETF" "https://tools.ietf.org/html/rfc2183"))
     
     (list 
         ; Socket
@@ -28,14 +27,12 @@
         (placeholder '(sendmail-connected? connection) "Should return true if the connection is still open")
         
         ; Send Mail
-        (placeholder '(sendmail-send-message-full connection message-content from to-list cc-list bcc-list headers message-options to-list-options) "Send a message to the server. The cc-list and bcc-list are optional. The headers hash is optional. The message-options and the to-list-options are optional. The to-list-options is a list of option tuple lists, one for each receiver. The function should return a list corresponding to the responses from the server for each recipient in the to-list. If there is only a single response, a list with a single response should be returned.")
+        (placeholder '(sendmail-send-message-full connection message-content from to-list cc-list bcc-list headers attachments message-options to-list-options) "Send a message to the server. The cc-list and bcc-list are optional. The headers hash is optional. The message-options and the to-list-options are optional. The to-list-options is a list of option tuple lists, one for each receiver. The function should return a list corresponding to the responses from the server for each recipient in the to-list. If there is only a single response, a list with a single response should be returned.")
          
         (define (sendmail-send-message-with-options connection message-content from to-list message-options to-list-options) 
-            (sendmail-send-message-full connection message-content from to-list '() '() (make-hash-table) message-options to-list-options))
+            (sendmail-send-message-full connection message-content from to-list '() '() (make-hash-table) (make-hash-table) message-options to-list-options))
         (define (sendmail-send-message connection content from to-list)
             (sendmail-send-message-with-options connection content from to-list  '() '()))
-        (define (sendmail-send-message-with-headers connection content from to-list headers-hash-map)
-            (sendmail-send-message-full connection content from to-list '() '() headers-hash-map '() '()))
         
         ; Response accessors
         (placeholder '(send-success? response) "Return whether the sending was successful.")
@@ -67,6 +64,19 @@
         (define (server-message-contains? content)
                 (string-contains? (server-message-data server) content))
 
+        (define (assert-server-message-contains? content message-property-description)
+                (assert 
+                    (server-message-contains? content)
+                    (string-append "Expected server to receive message with " message-property-description ", but received: " (server-message-data server))))
+
+        (define (assert-server-message-contains-ci? content message-property-description)
+                (assert 
+                    (server-message-contains-ci? content)
+                    (string-append "Expected server to receive message with " message-property-description ", but received: " (server-message-data server))))
+
+        (define (server-message-contains-ci? content)
+                (string-contains-ci? (server-message-data server) content))
+
         (setup (lambda ()  
             (set! server '())))
 
@@ -84,7 +94,7 @@
             (setup (lambda ()
                 (set! server (start-mock-server))
                 (server-set-extensions! server '("STARTTLS"))
-            (server-set-auths! server '(("LOGIN" ("account" "password"))))
+                (server-set-auths! server '(("LOGIN" ("account" "password"))))
                 (define (login-auth-proc credentials connection success failure)
                     (let 
                         ((login-user-response
@@ -178,9 +188,9 @@
 
             (test "Send a message to cc recipients" (lambda () 
                 (let
-                    ((responses (sendmail-send-message-full smtp-connection "message content" "sender@sender.to" '() '("user1@recipient.to") '() (make-hash-table) '() '())))
+                    ((responses (sendmail-send-message-full smtp-connection "message content" "sender@sender.to" '() '("user1@recipient.to") '() (make-hash-table) (make-hash-table) '() '())))
                     (assert (all? send-success? responses))
-                    (assert (server-message-contains? "user1@recipient.to"))
+                    (assert-server-message-contains? "user1@recipient.to" "cc recipient")
                     (assert
                         (any?
                             (lambda (request) 
@@ -190,7 +200,7 @@
 
             (test "Send a message to bcc recipients" (lambda () 
                 (let
-                    ((responses (sendmail-send-message-full smtp-connection "message content" "sender@sender.to" '() '() '("user1@recipient.to") (make-hash-table) '() '())))
+                    ((responses (sendmail-send-message-full smtp-connection "message content" "sender@sender.to" '() '() '("user1@recipient.to") (make-hash-table) (make-hash-table) '() '())))
                     (assert (all? send-success? responses))
                     (assert (not (server-message-contains? "user1@recipient.to")))
                     (assert
@@ -273,26 +283,22 @@
                 (sendmail-disconnect smtp-connection)
                 (set! smtp-connection '())))
 
+            (define (sendmail-send-with-headers headers)
+                (sendmail-send-message-full 
+                    smtp-connection "message content" "sender@sender.to" '("user@recipient.to") '() '() (alist->hash-table headers) (make-hash-table) '() '()))
+
             (test "set basic header" (lambda ()
-                (sendmail-send-message-with-headers smtp-connection "message content" "sender@sender.to" '("user@recipient.to") (alist->hash-table '(("x-my-header" "some value"))))
-                (assert (server-message-contains? "x-my-header: some value") (string-append "Expected x-my-header to be present, but instead got " (server-message-data server)))))
+                (sendmail-send-with-headers '(("x-my-header" "some value")))
+                (assert-server-message-contains? "x-my-header" "x-my-header present")))
 
             (test "set header with unicode value" (lambda ()
-                (sendmail-send-message-with-headers smtp-connection "message content" "sender@sender.to" '("user@recipient.to") (alist->hash-table '(("x-my-header" "¡some value"))))
-                (assert 
-                    (or
-                        (server-message-contains? "x-my-header: =?utf-8?q?=C2=A1some?= value")
-                        (server-message-contains? "x-my-header: =?utf-8?b?wqFzb21lIHZhbHVl?=")
-                        (server-message-contains? "x-my-header: =?UTF-8?Q?=C2=A1some?= value")
-                        (server-message-contains? "x-my-header: =?UTF-8?B?wqFzb21lIHZhbHVl?="))
-                    (string-append "Expected x-my-header to contain encoded ¡, but instead got " (server-message-data server)))
-                (assert
-                    (server-message-contains? "message content")
-                    (string-append "Expected message content to be unaltered by unicode header value, but instead got" (server-message-data server)))))
+                (sendmail-send-with-headers '(("x-my-header" "¡some value")))
+                (assert-server-message-contains? "x-my-header: =?utf-8?q?=C2=A1some?= value" "x-my-header containing encoded ¡")
+                (assert-server-message-contains? "message content" "unaltered message content despite unicode header value")))
 
             (test "set override standard header" (lambda ()
-                (sendmail-send-message-with-headers smtp-connection "message content" "sender@sender.to" '("user@recipient.to") (alist->hash-table '(("To" "another-user@recipient.to"))))
-                (assert (server-message-contains? "To: another-user@recipient.to") (string-append "Expected To header field to include another-user..., but instead got " (server-message-data server)))))
+                (sendmail-send-with-headers '(("To" "another-user@recipient.to")))
+                (assert-server-message-contains? "To: another-user@recipient.to" "header field that includes another-user@recipient.to")))
 
             (capability 'crlf-injection (list
 
@@ -302,14 +308,14 @@
                         '(("1some\rvalue") ("2some\nvalue") ("3some\r\nvalue"))
                         (lambda (header-value)
                             (let 
-                                ((responses (sendmail-send-message-with-headers smtp-connection "message content" "sender@sender.to" '("user@recipient.to") (alist->hash-table (list (list "x-my-header" header-value))))))
+                                ((responses (sendmail-send-with-headers (list (list "x-my-header" header-value)))))
                                 (assert (all? send-error? responses) (string-append "The header value: " header-value " should have resulted in error but did not:" responses)))))
 
                     (data-test "CRLF detection in unicode header value" 
                         '(("1¡some\rvalue") ("2¡some\nvalue") ("3¡some\r\nvalue"))
                         (lambda (header-value)
                             (let 
-                                ((responses (sendmail-send-message-with-headers smtp-connection "message content" "sender@sender.to" '("user@recipient.to") (alist->hash-table (list (list "x-my-header" header-value))))))
+                                ((responses (sendmail-send-with-headers (list (list "x-my-header" header-value)))))
                                 (assert (all? send-error? responses) (string-append "The header value: " header-value " should have resulted in error but did not:" responses)))))
 
                 ))
@@ -320,7 +326,7 @@
                         '(("1some\rvalue") ("2some\nvalue") ("3some\r\nvalue"))
                         (lambda (header-value)
                             (let 
-                                ((responses (sendmail-send-message-with-headers smtp-connection "message content" "sender@sender.to" '("user@recipient.to") (alist->hash-table (list (list "x-my-header" header-value))))))
+                                ((responses (sendmail-send-with-headers (list (list "x-my-header" header-value)))))
                                 (assert (all? send-success? responses) (string-append "Message was not sent successfully, instead got: " responses))
                                 (assert (not (server-message-contains? header-value)) (string-append "The header value: " header-value " should have been stripped of CRLF but did not:" (server-message-data server))))))
 
@@ -328,7 +334,7 @@
                         '(("1¡some \rvalue" "\rvalue") ("2¡some \nvalue" "\nvalue") ("3¡some \r\nvalue" "\r\nvalue"))
                         (lambda (header-value fragment)
                             (let 
-                                ((responses (sendmail-send-message-with-headers smtp-connection "message content" "sender@sender.to" '("user@recipient.to") (alist->hash-table (list (list "x-my-header" header-value))))))
+                                ((responses (sendmail-send-with-headers (list (list "x-my-header" header-value)))))
                                 (assert (all? send-success? responses) (string-append "Message was not sent successfully, instead got: " responses))
                                 (assert (not (server-message-contains? fragment)) (string-append "The header value: " header-value " should have been stripped of CRLF but did not: " (server-message-data server))))))
 
@@ -337,6 +343,141 @@
 
         ))
 
+        (capability 'attachments (list
+
+            (define smtp-connection '())
+            (define (connect-smtp-server)
+                (set! smtp-connection (sendmail-connect "localhost" (server-port server))))
+
+            (setup (lambda () 
+                (set! server (start-mock-server))
+                (connect-smtp-server)))
+
+            (tearDown (lambda ()
+                (sendmail-disconnect smtp-connection)
+                (set! smtp-connection '())))
+
+            ; attachments-properties is a list of alists with the following keys: 
+            ; "data", "file-name", "content-type", or "content-disposition"
+            (define sendmail-send-with-attachments (lambda attachments-properties
+                (let 
+                    ((properties-hashs (map alist->hash-table attachments-properties)))
+                    (for-each 
+                        (lambda (property-hash)
+                            (if (not (hash-table-exists? property-hash "content-disposition"))
+                                (hash-table-set! property-hash "content-disposition" "attachment")))
+                        properties-hashs)
+                    (sendmail-send-message-full 
+                        smtp-connection
+                        "message content" "sender@sender.to" '("recipient@recipient.to")
+                        '() '()
+                        (make-hash-table)
+                        properties-hashs
+                        '() '()))))
+                
+            (test "basic single text attachment" (lambda ()
+                (sendmail-send-with-attachments 
+                    '(("data" "info.txt")
+                      ("file-name" "info.txt")
+                      ("content-type" "text/plain")))
+                (assert 
+                    (or
+                        (server-message-contains? "content of info file")
+                        (server-message-contains? "Y29udGVudCBvZiBpbmZvIGZpbGU=")) 
+                    (string-append "Expected server to receive message with text attachment, but received: " (server-message-data server)))
+                (assert 
+                    (server-message-contains-ci? "content-disposition: attachment")
+                    (string-append "Expected server to receive message with content-disposition: attachment, but received: " (server-message-data server)))))
+
+            (test "basic multiple text attachments" (lambda ()
+                (sendmail-send-with-attachments 
+                    '(("data" "info.txt")
+                      ("file-name" "info.txt")
+                      ("content-type" "text/plain"))
+                    '(("data" "info.txt") 
+                      ("file-name" "second-info.txt")
+                      ("content-type" "text/plain")))
+                (assert 
+                    (and (server-message-contains-ci? "info.txt") (server-message-contains-ci? "second-info.txt"))
+                    (string-append "Expected server to receive message with two attachments, but received: " (server-message-data server)))))
+
+            (test "basic image attachment" (lambda ()
+                (sendmail-send-with-attachments 
+                    '(("data" "test.png")
+                      ("file-name" "test.png")
+                      ("content-type" "image/png")))
+                (assert 
+                    ; only part of base64 encoded image
+                    (server-message-contains? "iVBORw0KGgoAAAANSUhEUgAAAAIAAAACCAIAAAD91JpzAAAAAXNSR0IArs4c6QAAAARnQU1BAACx")  
+                    (string-append "Expected server to receive message with image attachment, but received: " (server-message-data server)))
+                (assert 
+                    (server-message-contains-ci? "content-disposition: attachment")
+                    (string-append "Expected server to receive message with content-disposition: attachment, but received: " (server-message-data server)))))
+
+            (test "multiple attachments with same name" (lambda ()
+                (sendmail-send-with-attachments
+                    '(("data" "info.txt") 
+                      ("file-name" "info.txt")
+                      ("content-type" "text/plain"))
+                      
+                    '(("data" "info.txt")
+                      ("file-name" "info.txt")
+                      ("content-type" "text/plain")))
+                (assert 
+                    (= 2 (length (string-contains-every? (server-message-data server) "info.txt"))) 
+                    (string-append "Expected server to receive message with two text attachments with the same name, but received: " (server-message-data server)))))
+
+            ; Filename property is optional: https://datatracker.ietf.org/doc/html/rfc2183#section-1
+            (test "attachment without a name" (lambda ()
+                (sendmail-send-with-attachments
+                    '(("data" "info.txt")
+                      ("content-type" "text/plain")))
+                (assert-server-message-contains-ci? "content-disposition: attachment" "an attachment")
+                (assert
+                    (not (server-message-contains-ci? "info.txt"))
+                    (string-append "Expected server to receive a message with an attachment without a name, but received: " (server-message-data server)))))
+
+            (test "image attachment with inline disposition" (lambda ()
+                (sendmail-send-with-attachments
+                    '(("data" "test.png")
+                      ("file-name" "test.png")
+                      ("content-type" "image/png")
+                      ("content-disposition" "inline")))
+                (assert-server-message-contains-ci? "content-disposition: inline" "inline attachment")))
+
+            (test "text attachment with inline disposition" (lambda ()
+                (sendmail-send-with-attachments
+                    '(("data" "info.txt")
+                      ("file-name" "info.txt")
+                      ("content-type" "text/plain")
+                      ("content-disposition" "inline")))
+                (assert-server-message-contains-ci? "content-disposition: inline" "inline attachment")))
+
+            ; - inline attachment with cid? https://www.rfc-editor.org/rfc/rfc2392
+            ; => non-trivial as we either need to do it completely manually or use a template engine. A template engine has 
+            ; custom syntax, so we can not create a general scenario for it
+
+            (capability 'automatic-mime-detection (list
+
+                ; This is difficult to test, as we would need to find the attachment MIME part and check 
+                ; the MIME type of the attachment.
+
+            ))
+
+            (capability 'unicode-file-name (list
+
+                (test "basic single text attachment with unicode file name" (lambda ()
+                    (sendmail-send-with-attachments 
+                        '(("data" "info.txt")
+                          ("file-name" "info¡.txt")
+                          ("content-type" "text/plain")))
+                    (assert-server-message-contains-ci? "utf-8''info%C2%A1.txt" "unicode file name")))
+
+
+            ))
+
+        ))
+
         (capability 'general-crlf-injection (list
 
             (define smtp-connection '())
@@ -462,10 +603,7 @@
                                 smtp-connection "¡a test message containing unicode!" "sender@sender.com" '("user@recipient.com") '("BODY=8BITMIME") '())))
                             (assert (all? send-success? send-message-responses))
                             (assert-any-request server "MAIL FROM:<sender@sender.com> BODY=8BITMIME")
-                            (assert 
-                                (server-message-contains? "¡a test message containing unicode!")
-                                (string-append 
-                                    "Expected server to receive message with unicode content directly, but received: " (server-message-data server))))))
+                            (assert-server-message-contains? "¡a test message containing unicode!" "unicode content"))))
                 
                 ))
 
@@ -489,10 +627,7 @@
                                 smtp-connection "¡a test message containing unicode!" "sender@sender.com" '("user@recipient.com") '() '())))
                             (assert (all? send-success? send-message-responses))
                             (assert-any-request server "MAIL FROM:<sender@sender.com> BODY=8BITMIME")
-                            (assert 
-                                (server-message-contains? "¡a test message containing unicode!")
-                                (string-append 
-                                    "Expected server to receive message with unicode content directly, but received: " (server-message-data server))))))
+                            (assert-server-message-contains? "¡a test message containing unicode!" "unicode content directly"))))
                 
                 ))
             ))
diff --git a/rosetta-test/interpreter-tests.json b/rosetta-test/interpreter-tests.json
index 0daa483..87e7f9f 100644
--- a/rosetta-test/interpreter-tests.json
+++ b/rosetta-test/interpreter-tests.json
@@ -116,5 +116,13 @@
     {"input": "(begin (hash-table-ref! ht 'c 3) (hash-table-ref ht 'c))", "expected": 3},
     {"input": "(hash-table->alist ht)", "expected": [["b", 2], ["c", 3]]},
     {"input": "(hash-table->alist (make-hash-table))", "expected": []},
-    {"input": "(hash-table-ref (alist->hash-table '((a 10) (b 20))) 'b)", "expected": 20}
+    {"input": "(hash-table-ref (alist->hash-table '((a 10) (b 20))) 'b)", "expected": 20},
+    {"input": "(substring \"abc\" 0 1)", "expected": "a"},
+    {"input": "(substring \"abc\" 0 2)", "expected": "ab"},
+    {"input": "(substring \"abc\" 0 3)", "expected": "abc"},
+    {"input": "(substring \"abc\" 1 3)", "expected": "bc"},
+    {"input": "(substring \"abc\" 0 0)", "expected": ""},
+    {"input": "(substring \"abc\" 2 2)", "expected": ""},
+    {"input": "(substring \"abc\" 3 4)", "expected": {"type": "Error"}},
+    {"input": "(string-contains-every? \"abvabab\" \"ab\")", "expected": [0,3,5]}
 ]
\ No newline at end of file
diff --git a/rosetta-test/stdlib.scm b/rosetta-test/stdlib.scm
index 924eef1..ab5ff17 100644
--- a/rosetta-test/stdlib.scm
+++ b/rosetta-test/stdlib.scm
@@ -285,9 +285,42 @@
                     (string-index-help (cdr str) substr (+ index 1)))))
         (string-index-help str substr 0))
 
+    (define (substring str start end)
+        (if (or (< start 0) (< end 0) (> start (length str)) (> end (length str)))
+            (throw (error "substring: out of bounds")))
+        (if (= start end)
+            ""
+            (begin
+                (define (substring-help-to-end str pos end res)
+                    (if (or (empty? str) (= pos end)) 
+                        res
+                        (substring-help-to-end (cdr str) (+ pos 1) end (string-append res (car str)))))
+                (define (substring-help-from-start str start pos)
+                    (if (= start pos)
+                        str
+                        (substring-help-from-start (cdr str) start (+ pos 1))))
+                (substring-help-to-end 
+                    (substring-help-from-start str start 0) 
+                    0 end ""))))
+
     (define (string-contains? str substr)
         (if (string-index str substr) #t #f))
     
     (define (string-contains-ci? str substr)
-        (if (string-index-ci (string-downcase str) (string-downcase substr)) #t #f))
+        (if (string-index (string-downcase str) (string-downcase substr)) #t #f))
+
+    (define (string-contains-every? str substr)
+        (define result '())
+        (define (string-index-help str substr index)
+            (if (empty? str)
+                result
+                (begin
+                    (if (string-prefix? substr str) 
+                        (set! result (append result (list index))))
+                    (string-index-help (cdr str) substr (+ index 1)))))
+        (string-index-help str substr 0))
+
+    (define (string-contains-every-ci? str substr)
+        (string-contains-every? (string-downcase str) (string-downcase substr)))
+
 )
\ No newline at end of file