From fa4b1ddcf09174c49c21e42a298ec97d63886c5e Mon Sep 17 00:00:00 2001
From: Jack Grigg <jack@electriccoin.co>
Date: Mon, 25 Jan 2021 11:04:26 +0000
Subject: [PATCH] ZIP 311: Use length(a) instead of a.len()

---
 zip-0311.html | 41 ++++++++++++++++++++++++++---------------
 zip-0311.rst  | 30 +++++++++++++++---------------
 2 files changed, 41 insertions(+), 30 deletions(-)

diff --git a/zip-0311.html b/zip-0311.html
index 6ae8faba..4fd5b260 100644
--- a/zip-0311.html
+++ b/zip-0311.html
@@ -175,7 +175,7 @@ Discussions-To: &lt;<a href="https://github.com/zcash/zips/issues/387">https://g
                     <span class="math">\(b\)</span>
                 .</li>
                 <li>
-                    <span class="math">\(a\text{.len}()\)</span>
+                    <span class="math">\(\mathsf{length}(a)\)</span>
                  means the length of the vector
                     <span class="math">\(a\)</span>
                 .</li>
@@ -189,11 +189,14 @@ Discussions-To: &lt;<a href="https://github.com/zcash/zips/issues/387">https://g
                     <li><cite>msg</cite>: A message field, which could contain a challenge value from the party to whom the payment disclosure is directed.</li>
                     <li>
                         <span class="math">\(\mathsf{saplingOutputs}\)</span>
-                    : A vector of the Sapling Outputs that we are disclosing [0..tx.shieldedOutputs.len()]
+                    : A vector of the Sapling Outputs that we are disclosing
+                        <span class="math">\([0..\mathsf{length}(\mathsf{tx.shieldedOutputs})]\)</span>
                         <ul>
                             <li>
                                 <span class="math">\(\mathsf{index}\)</span>
-                            : An index into <cite>tx.shieldedOutputs</cite>.</li>
+                            : An index into
+                                <span class="math">\(\mathsf{tx.shieldedOutputs}\)</span>
+                            .</li>
                             <li>
                                 <span class="math">\(\mathsf{ock}\)</span>
                             : The outgoing cipher key that allows this output to be recovered. <a id="id4" class="footnote_reference" href="#protocol-saplingencrypt">5</a></li>
@@ -201,11 +204,14 @@ Discussions-To: &lt;<a href="https://github.com/zcash/zips/issues/387">https://g
                     </li>
                     <li>
                         <span class="math">\(\mathsf{saplingSpends}\)</span>
-                    : A vector of the Sapling Spends for which we are proving spend authority [0..tx.shieldedSpends.len()]
+                    : A vector of the Sapling Spends for which we are proving spend authority
+                        <span class="math">\([0..\mathsf{length}(\mathsf{tx.shieldedSpends})]\)</span>
                         <ul>
                             <li>
                                 <span class="math">\(\mathsf{index}\)</span>
-                            : An index into <cite>tx.shieldedSpends</cite>.</li>
+                            : An index into
+                                <span class="math">\(\mathsf{tx.shieldedSpends}\)</span>
+                            .</li>
                             <li>
                                 <span class="math">\(\mathsf{cv}\)</span>
                             : A value commitment to the spent note.</li>
@@ -237,11 +243,14 @@ Discussions-To: &lt;<a href="https://github.com/zcash/zips/issues/387">https://g
                     </li>
                     <li>
                         <span class="math">\(\mathsf{transparentInputs}\)</span>
-                    : A vector of the transparent inputs for which we are proving spend authority [0..tx.vin.len()]
+                    : A vector of the transparent inputs for which we are proving spend authority
+                        <span class="math">\([0..\mathsf{length}(\mathsf{tx.vin})]\)</span>
                         <ul>
                             <li>
                                 <span class="math">\(\mathsf{index}\)</span>
-                            : An index into <cite>tx.vin</cite>.</li>
+                            : An index into
+                                <span class="math">\(\mathsf{tx.vin}\)</span>
+                            .</li>
                             <li>
                                 <span class="math">\(\mathsf{sig}\)</span>
                             : A BIP 322 signature. <a id="id6" class="footnote_reference" href="#bip-0322">8</a>
@@ -282,7 +291,9 @@ Discussions-To: &lt;<a href="https://github.com/zcash/zips/issues/387">https://g
                         <ul>
                             <li>
                                 <span class="math">\(\mathsf{index}\)</span>
-                            : An index into <cite>tx.vin</cite>.</li>
+                            : An index into
+                                <span class="math">\(\mathsf{tx.vin}\)</span>
+                            .</li>
                             <li>The inputs to a BIP 322 signature (excluding <cite>message_data</cite>).</li>
                         </ul>
                     </li>
@@ -357,13 +368,13 @@ Discussions-To: &lt;<a href="https://github.com/zcash/zips/issues/387">https://g
                             <li>Vector length correctness:
                                 <ul>
                                     <li>
-                                        <span class="math">\(\mathsf{pd.saplingOutputs.len}() \leq \mathsf{tx.shieldedOutputs.len}()\)</span>
+                                        <span class="math">\(\mathsf{length}(\mathsf{pd.saplingOutputs}) \leq \mathsf{length}(\mathsf{tx.shieldedOutputs})\)</span>
                                     </li>
                                     <li>
-                                        <span class="math">\(\mathsf{pd.saplingSpends.len}() \leq \mathsf{tx.shieldedSpends.len}()\)</span>
+                                        <span class="math">\(\mathsf{length}(\mathsf{pd.saplingSpends}) \leq \mathsf{length}(\mathsf{tx.shieldedSpends})\)</span>
                                     </li>
                                     <li>
-                                        <span class="math">\(\mathsf{pd.transparentInputs.len}() \leq \mathsf{tx.vin.len}()\)</span>
+                                        <span class="math">\(\mathsf{length}(\mathsf{pd.transparentInputs}) \leq \mathsf{length}(\mathsf{tx.vin})\)</span>
                                     </li>
                                 </ul>
                             </li>
@@ -399,26 +410,26 @@ Discussions-To: &lt;<a href="https://github.com/zcash/zips/issues/387">https://g
                                      in
                                         <span class="math">\(\mathsf{pd.saplingOutputs}\)</span>
                                     ,
-                                        <span class="math">\(\mathsf{output.index} &lt; \mathsf{tx.shieldedOutputs.len}()\)</span>
+                                        <span class="math">\(\mathsf{output.index} &lt; \mathsf{length}(\mathsf{tx.shieldedOutputs})\)</span>
                                     </li>
                                     <li>For every
                                         <span class="math">\(\mathsf{spend}\)</span>
                                      in
                                         <span class="math">\(\mathsf{pd.saplingSpends}\)</span>
                                     ,
-                                        <span class="math">\(\mathsf{spend.index} &lt; \mathsf{tx.shieldedSpends.len}()\)</span>
+                                        <span class="math">\(\mathsf{spend.index} &lt; \mathsf{length}(\mathsf{tx.shieldedSpends})\)</span>
                                     </li>
                                     <li>For every
                                         <span class="math">\(\mathsf{input}\)</span>
                                      in
                                         <span class="math">\(\mathsf{pd.transparentInputs}\)</span>
                                     ,
-                                        <span class="math">\(\mathsf{input.index} &lt; \mathsf{tx.vin.len}()\)</span>
+                                        <span class="math">\(\mathsf{input.index} &lt; \mathsf{length}(\mathsf{tx.vin})\)</span>
                                     </li>
                                 </ul>
                             </li>
                             <li>
-                                <span class="math">\(\mathsf{pd.saplingSpends.len}() + \mathsf{pd.transparentInputs.len}() &gt; 0\)</span>
+                                <span class="math">\(\mathsf{length}(\mathsf{pd.saplingSpends}) + \mathsf{length}(\mathsf{pd.transparentInputs}) &gt; 0\)</span>
                             </li>
                         </ul>
                     </li>
diff --git a/zip-0311.rst b/zip-0311.rst
index ddc15729..6ff6e103 100644
--- a/zip-0311.rst
+++ b/zip-0311.rst
@@ -160,7 +160,7 @@ We also define the following notation here:
 - :math:`[a..b]` means the sequence of values inclusive of :math:`a` and exclusive of
   :math:`b`.
 
-- :math:`a\text{.len}()` means the length of the vector :math:`a`.
+- :math:`\mathsf{length}(a)` means the length of the vector :math:`a`.
 
 
 Specification
@@ -177,16 +177,16 @@ A payment disclosure has the following fields:
   the payment disclosure is directed.
 
 - :math:`\mathsf{saplingOutputs}`: A vector of the Sapling Outputs that we are disclosing
-  [0..tx.shieldedOutputs.len()]
+  :math:`[0..\mathsf{length}(\mathsf{tx.shieldedOutputs})]`
 
-  - :math:`\mathsf{index}`: An index into `tx.shieldedOutputs`.
+  - :math:`\mathsf{index}`: An index into :math:`\mathsf{tx.shieldedOutputs}`.
   - :math:`\mathsf{ock}`: The outgoing cipher key that allows this output to be recovered.
     [#protocol-saplingencrypt]_
 
 - :math:`\mathsf{saplingSpends}`: A vector of the Sapling Spends for which we are proving
-  spend authority [0..tx.shieldedSpends.len()]
+  spend authority :math:`[0..\mathsf{length}(\mathsf{tx.shieldedSpends})]`
 
-  - :math:`\mathsf{index}`: An index into `tx.shieldedSpends`.
+  - :math:`\mathsf{index}`: An index into :math:`\mathsf{tx.shieldedSpends}`.
   - :math:`\mathsf{cv}`: A value commitment to the spent note.
   - :math:`\mathsf{rk}`: A randomized public key linked to the spent note.
   - :math:`\mathsf{zkproof_{spend}}`: A Sapling spend proof.
@@ -199,9 +199,9 @@ A payment disclosure has the following fields:
   - :math:`\mathsf{spendAuthSig}`
 
 - :math:`\mathsf{transparentInputs}`: A vector of the transparent inputs for which we are
-  proving spend authority [0..tx.vin.len()]
+  proving spend authority :math:`[0..\mathsf{length}(\mathsf{tx.vin})]`
 
-  - :math:`\mathsf{index}`: An index into `tx.vin`.
+  - :math:`\mathsf{index}`: An index into :math:`\mathsf{tx.vin}`.
   - :math:`\mathsf{sig}`: A BIP 322 signature. [#bip-0322]_
 
     - TODO: `zcashd` currently only supports the legacy format defined in BIP 322. We may
@@ -232,7 +232,7 @@ The inputs to a payment disclosure are:
 
 - A vector of transparent input tuples (which may be empty) containing:
 
-  - :math:`\mathsf{index}`: An index into `tx.vin`.
+  - :math:`\mathsf{index}`: An index into :math:`\mathsf{tx.vin}`.
   - The inputs to a BIP 322 signature (excluding `message_data`).
 
 The caller MUST provide at least one input tuple of any type (either a Sapling spend tuple
@@ -291,9 +291,9 @@ by the caller), the verifier proceeds as follows:
 
   - Vector length correctness:
 
-    - :math:`\mathsf{pd.saplingOutputs.len}() \leq \mathsf{tx.shieldedOutputs.len}()`
-    - :math:`\mathsf{pd.saplingSpends.len}() \leq \mathsf{tx.shieldedSpends.len}()`
-    - :math:`\mathsf{pd.transparentInputs.len}() \leq \mathsf{tx.vin.len}()`
+    - :math:`\mathsf{length}(\mathsf{pd.saplingOutputs}) \leq \mathsf{length}(\mathsf{tx.shieldedOutputs})`
+    - :math:`\mathsf{length}(\mathsf{pd.saplingSpends}) \leq \mathsf{length}(\mathsf{tx.shieldedSpends})`
+    - :math:`\mathsf{length}(\mathsf{pd.transparentInputs}) \leq \mathsf{length}(\mathsf{tx.vin})`
 
   - Index uniqueness:
 
@@ -307,13 +307,13 @@ by the caller), the verifier proceeds as follows:
   - Index correctness:
 
     - For every :math:`\mathsf{output}` in :math:`\mathsf{pd.saplingOutputs}`,
-      :math:`\mathsf{output.index} < \mathsf{tx.shieldedOutputs.len}()`
+      :math:`\mathsf{output.index} < \mathsf{length}(\mathsf{tx.shieldedOutputs})`
     - For every :math:`\mathsf{spend}` in :math:`\mathsf{pd.saplingSpends}`,
-      :math:`\mathsf{spend.index} < \mathsf{tx.shieldedSpends.len}()`
+      :math:`\mathsf{spend.index} < \mathsf{length}(\mathsf{tx.shieldedSpends})`
     - For every :math:`\mathsf{input}` in :math:`\mathsf{pd.transparentInputs}`,
-      :math:`\mathsf{input.index} < \mathsf{tx.vin.len}()`
+      :math:`\mathsf{input.index} < \mathsf{length}(\mathsf{tx.vin})`
 
-  - :math:`\mathsf{pd.saplingSpends.len}() + \mathsf{pd.transparentInputs.len}() > 0`
+  - :math:`\mathsf{length}(\mathsf{pd.saplingSpends}) + \mathsf{length}(\mathsf{pd.transparentInputs}) > 0`
 
 - Let :math:`unsignedPaymentDisclosure` be the encoding of the payment disclosure without
   signatures.