diff --git a/README.pdf b/README.pdf
index af4bbfb..b52ee09 100644
Binary files a/README.pdf and b/README.pdf differ
diff --git a/README.tex b/README.tex
index fa72d97..b8f441c 100644
--- a/README.tex
+++ b/README.tex
@@ -75,7 +75,7 @@ The entire program revolves around the main struct defined as:\\
 ; - output: String\\
 ; - program: Program\\
 ; - ip: InstructionPointer\\
-; - error: Option<ErrorCode>\\
+; - error: Option<String>\\
 ; Interpretation: the current state of execution of a brainf*ck program.\\ \\
 \textbf{\large (struct prog-state (tape dp tape-len output program ip error)}}
 
@@ -94,14 +94,16 @@ And, likewise, each term in the struct has its own type definition: \\
 ; - "+" (add1)\\
 ; - "-" (sub1)\\
 ; - "." (out)\\
-; - ","\\
+; - "," (in)\\
 ; - "[" (loop-start)\\
 ; - "]" (loop-end)\\
 ; Interpretation: the brainf*ck program.\\\\
 ; A InstructionPointer (IP) is a NonNegInt\\
 ; Interpretation: a pointer to the instruction to execute.\\\\
 ; An ErrorCode is one of:\\
-; - 'error1\\
+; - 'error1 (Interp: negative tape position when <)\\
+; - 'error2 (Interp: non-matching [)\\
+; - 'error3 (Interp: non-matching ])\\
 ; Interpretation: an error code for the bf interpreter.}
 
 \subsubsection{Execute Function}
@@ -129,7 +131,7 @@ List of helper functions for execute:
 
 \item[] \textbf{\large \texttt{exec-sub1}}:\\ ProgState -$>$ ProgState\\ Given a ProgState, returns a new ProgState with the $-$ instruction executed.
 
-\item[] \textbf{\large \texttt{exec-out}}:\\ ProgState -$>$ ProgState\\ Given a ProgState, returns a new ProgState with the . instruction executed.
+\item[] \textbf{\large \texttt{exec-out}}:\\ ProgState -$>$ ProgState\\ Given a ProgState, returns a new ProgState with the $.$ instruction executed.
 
 \item[] \textbf{\large \texttt{exec-loop-start}}:\\ ProgState -$>$ ProgState\\ Given a ProgState, returns a new ProgState with the $[$ instruction executed.
 
diff --git a/interpreter.rkt b/interpreter.rkt
index 570b8a8..dbd5d79 100644
--- a/interpreter.rkt
+++ b/interpreter.rkt
@@ -29,7 +29,7 @@
 ; - "+" (add1)
 ; - "-" (sub1)
 ; - "." (out)
-; - ","
+; - "," (in)
 ; - "[" (loop-start)
 ; - "]" (loop-end)
 ; Interpretation: the brainf*ck program.
@@ -38,7 +38,9 @@
 ; Interpretation: a pointer to the instruction to execute.
 
 ; An ErrorCode is one of:
-; - 'error1
+; - 'error1 (Interp: negative tape position when <)
+; - 'error2 (Interp: non-matching [)
+; - 'error3 (Interp: non-matching ])
 ; Interp: an error code for the bf interpreter.
 
 ; A ProgState is a (prog-state tape dp output program ip) where:
@@ -48,7 +50,7 @@
 ; - output: String
 ; - program: Program
 ; - ip: InstructionPointer
-; - error: Option<ErrorCode>
+; - error: Option<String>
 ; Interpretation: the current state of execution of a brainf*ck program.
 (struct prog-state (tape dp tape-len output program ip error)
   #:transparent