More detail in a few help pages

14 files changed, 51 insertions, 17 deletions

diff --git a/docs/help/depth.html b/docs/help/depth.html
index 03fcaea6..4657a433 100644
--- a/docs/help/depth.html
+++ b/docs/help/depth.html
@@ -7,10 +7,13 @@
 <h1 id="circle-with-two-dots-"><a class="header" href="#circle-with-two-dots-">Circle With Two Dots (<code><span class='Modifier2'>⚇</span></code>)</a></h1>
 <h2 id="𝔽𝕘-𝕩-𝕨-𝔽𝕘-𝕩-depth"><a class="header" href="#𝔽𝕘-𝕩-𝕨-𝔽𝕘-𝕩-depth"><code><span class='Function'>𝔽</span><span class='Modifier2'>⚇</span><span class='Value'>𝕘</span> <span class='Value'>𝕩</span></code>, <code><span class='Value'>𝕨</span> <span class='Function'>𝔽</span><span class='Modifier2'>⚇</span><span class='Value'>𝕘</span> <span class='Value'>𝕩</span></code>: Depth</a></h2>
 <p><a class="fulldoc" href="../doc/depth.html#the-depth-modifier">→full documentation</a></p>
-<p>Apply <code><span class='Function'>𝔽</span></code> to the cells of the arguments at depth given in <code><span class='Value'>𝕘</span></code>.</p>
-<a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=MeKKuOKGk+KahzEg4p+o4p+oMSwyLDPin6ksIOKfqDQsNSw24p+p4p+pCgoxIOKGk+KahzEg4p+o4p+oMSwyLDPin6ksIOKfqDQsNSw24p+p4p+p">↗️</a><pre>    <span class='Number'>1</span><span class='Modifier2'>⊸</span><span class='Function'>↓</span><span class='Modifier2'>⚇</span><span class='Number'>1</span> <span class='Bracket'>⟨⟨</span><span class='Number'>1</span><span class='Separator'>,</span><span class='Number'>2</span><span class='Separator'>,</span><span class='Number'>3</span><span class='Bracket'>⟩</span><span class='Separator'>,</span> <span class='Bracket'>⟨</span><span class='Number'>4</span><span class='Separator'>,</span><span class='Number'>5</span><span class='Separator'>,</span><span class='Number'>6</span><span class='Bracket'>⟩⟩</span>
+<p>Apply <code><span class='Function'>𝔽</span></code> to the cells of the arguments at depth given in <code><span class='Value'>𝕘</span></code>. Negative numbers count down from the top level and non-negative ones from the bottom up.</p>
+<a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=MeKKuOKGk+KahzEg4p+o4p+oMSwyLDPin6ksIOKfqDQsNSw24p+p4p+pCgoxIOKGk+KahzEg4p+o4p+oMSwyLDPin6ksIOKfqDQsNSw24p+p4p+pCgooK8K04oaVKeKahzAg4p+oMiw04oC/Nywz4p+pICAjIEltcGxlbWVudHMgcGVydmFzaW9u">↗️</a><pre>    <span class='Number'>1</span><span class='Modifier2'>⊸</span><span class='Function'>↓</span><span class='Modifier2'>⚇</span><span class='Number'>1</span> <span class='Bracket'>⟨⟨</span><span class='Number'>1</span><span class='Separator'>,</span><span class='Number'>2</span><span class='Separator'>,</span><span class='Number'>3</span><span class='Bracket'>⟩</span><span class='Separator'>,</span> <span class='Bracket'>⟨</span><span class='Number'>4</span><span class='Separator'>,</span><span class='Number'>5</span><span class='Separator'>,</span><span class='Number'>6</span><span class='Bracket'>⟩⟩</span>
 ⟨ ⟨ 2 3 ⟩ ⟨ 5 6 ⟩ ⟩
 
     <span class='Number'>1</span> <span class='Function'>↓</span><span class='Modifier2'>⚇</span><span class='Number'>1</span> <span class='Bracket'>⟨⟨</span><span class='Number'>1</span><span class='Separator'>,</span><span class='Number'>2</span><span class='Separator'>,</span><span class='Number'>3</span><span class='Bracket'>⟩</span><span class='Separator'>,</span> <span class='Bracket'>⟨</span><span class='Number'>4</span><span class='Separator'>,</span><span class='Number'>5</span><span class='Separator'>,</span><span class='Number'>6</span><span class='Bracket'>⟩⟩</span>
 ⟨ ⟨ 2 3 ⟩ ⟨ 5 6 ⟩ ⟩
+
+    <span class='Paren'>(</span><span class='Function'>+</span><span class='Modifier'>´</span><span class='Function'>↕</span><span class='Paren'>)</span><span class='Modifier2'>⚇</span><span class='Number'>0</span> <span class='Bracket'>⟨</span><span class='Number'>2</span><span class='Separator'>,</span><span class='Number'>4</span><span class='Ligature'>‿</span><span class='Number'>7</span><span class='Separator'>,</span><span class='Number'>3</span><span class='Bracket'>⟩</span>  <span class='Comment'># Implements pervasion
+</span>⟨ 1 ⟨ 6 21 ⟩ 3 ⟩
 </pre>
diff --git a/docs/help/leftargument.html b/docs/help/leftargument.html
index 2c92de98..58c60486 100644
--- a/docs/help/leftargument.html
+++ b/docs/help/leftargument.html
@@ -8,6 +8,16 @@
 <h2 id="𝕨-left-argument"><a class="header" href="#𝕨-left-argument"><code><span class='Value'>𝕨</span></code>: Left Argument</a></h2>
 <p><a class="fulldoc" href="../doc/syntax.html#blocks">→full documentation</a></p>
 <p>A variable assigned to the left argument of a block. <code><span class='Function'>𝕎</span></code> can be used to access the left argument as a function.</p>
-<a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=NSB78J2VqH0gMQ==">↗️</a><pre>    <span class='Number'>5</span> <span class='Brace'>{</span><span class='Value'>𝕨</span><span class='Brace'>}</span> <span class='Number'>1</span>
+<a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=NSB78J2VqH0gMQoKLeKAv8O3IHvwnZWO8J2VqX3CqCA0">↗️</a><pre>    <span class='Number'>5</span> <span class='Brace'>{</span><span class='Value'>𝕨</span><span class='Brace'>}</span> <span class='Number'>1</span>
 5
+
+    <span class='Function'>-</span><span class='Ligature'>‿</span><span class='Function'>÷</span> <span class='Brace'>{</span><span class='Function'>𝕎</span><span class='Value'>𝕩</span><span class='Brace'>}</span><span class='Modifier'>¨</span> <span class='Number'>4</span>
+⟨ ¯4 0.25 ⟩
+</pre>
+<p>In a call with no left argument, <code><span class='Value'>𝕨</span></code> functions as <a href="nothing.html">Nothing</a> and <code><span class='Function'>𝕎</span></code> can't be used.</p>
+<a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=eygt8J2VqCnii4jwnZWpfSA2CgoyIHsoLfCdlagp4ouI8J2VqX0gNg==">↗️</a><pre>    <span class='Brace'>{</span><span class='Paren'>(</span><span class='Function'>-</span><span class='Value'>𝕨</span><span class='Paren'>)</span><span class='Function'>⋈</span><span class='Value'>𝕩</span><span class='Brace'>}</span> <span class='Number'>6</span>
+⟨ 6 ⟩
+
+    <span class='Number'>2</span> <span class='Brace'>{</span><span class='Paren'>(</span><span class='Function'>-</span><span class='Value'>𝕨</span><span class='Paren'>)</span><span class='Function'>⋈</span><span class='Value'>𝕩</span><span class='Brace'>}</span> <span class='Number'>6</span>
+⟨ ¯2 6 ⟩
 </pre>
diff --git a/docs/help/length_notequals.html b/docs/help/length_notequals.html
index 3667e2fe..9efb3a35 100644
--- a/docs/help/length_notequals.html
+++ b/docs/help/length_notequals.html
@@ -25,6 +25,7 @@
 </pre>
 <h2 id="𝕨--𝕩-not-equal-to"><a class="header" href="#𝕨--𝕩-not-equal-to"><code><span class='Value'>𝕨</span> <span class='Function'>≠</span> <span class='Value'>𝕩</span></code>: Not Equal To</a></h2>
 <p><a class="fulldoc" href="../doc/arithmetic.html#comparisons">→full documentation</a></p>
+<p>Do argument atoms not match?</p>
 <p><a href="../doc/arithmetic.html#pervasion">Pervasive.</a></p>
 <a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=MSDiiaAgMwoKMuKAvzPigL8wIOKJoCAz4oC/MeKAvzAKCidhJyDiiaAgJ2En">↗️</a><pre>    <span class='Number'>1</span> <span class='Function'>≠</span> <span class='Number'>3</span>
 1
diff --git a/docs/help/merge_greaterthan.html b/docs/help/merge_greaterthan.html
index c0b21032..da588aa8 100644
--- a/docs/help/merge_greaterthan.html
+++ b/docs/help/merge_greaterthan.html
@@ -7,9 +7,8 @@
 <h1 id="greater-than-"><a class="header" href="#greater-than-">Greater Than (<code><span class='Function'>&gt;</span></code>)</a></h1>
 <h2 id="-𝕩-merge"><a class="header" href="#-𝕩-merge"><code><span class='Function'>&gt;</span> <span class='Value'>𝕩</span></code>: Merge</a></h2>
 <p><a class="fulldoc" href="../doc/couple.html">→full documentation</a></p>
-<p>Add the rank of an element of <code><span class='Value'>𝕩</span></code> to the rank of <code><span class='Value'>𝕩</span></code>.</p>
-<p>All elements must have the same rank.</p>
-<p>Returns atomic values as is.</p>
+<p>Combine an array of arrays into one array. All elements of <code><span class='Value'>𝕩</span></code> must have the same rank, and the result rank is that plus the rank of <code><span class='Value'>𝕩</span></code>.</p>
+<p>Returns and boxed atoms unchanged.</p>
 <a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=YSDihpAg4p+o4p+oMSwgMuKfqSwg4p+oMywgNOKfqeKfqQoKPmEKCuKJomEKCuKJoj5h">↗️</a><pre>    <span class='Value'>a</span> <span class='Gets'>←</span> <span class='Bracket'>⟨⟨</span><span class='Number'>1</span><span class='Separator'>,</span> <span class='Number'>2</span><span class='Bracket'>⟩</span><span class='Separator'>,</span> <span class='Bracket'>⟨</span><span class='Number'>3</span><span class='Separator'>,</span> <span class='Number'>4</span><span class='Bracket'>⟩⟩</span>
 
     <span class='Function'>&gt;</span><span class='Value'>a</span>
diff --git a/docs/help/nothing.html b/docs/help/nothing.html
index b83a26c4..f4361a83 100644
--- a/docs/help/nothing.html
+++ b/docs/help/nothing.html
@@ -7,6 +7,10 @@
 <h1 id="middle-dot-"><a class="header" href="#middle-dot-">Middle Dot (<code><span class='Nothing'>·</span></code>)</a></h1>
 <h2 id="-nothing"><a class="header" href="#-nothing"><code><span class='Nothing'>·</span></code>: Nothing</a></h2>
 <p><a class="fulldoc" href="../doc/expression.html#nothing">→full documentation</a></p>
+<p>Indicates no value. If a left argument is Nothing, the function is called with no left argument, and if the right is Nothing, it's not called and &quot;returns&quot; Nothing.</p>
+<a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=wrcg4oy9ICJhYmMiICAjIFJldmVyc2UgaW5zdGVhZCBvZiBSb3RhdGU=">↗️</a><pre>    <span class='Nothing'>·</span> <span class='Function'>⌽</span> <span class='String'>&quot;abc&quot;</span>  <span class='Comment'># Reverse instead of Rotate
+</span>"cba"
+</pre>
 <h3 id="in-trains"><a class="header" href="#in-trains">In Trains</a></h3>
 <p>Nothing can serve as a left argument in a train to string together multiple monadic functions.</p>
 <a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=KC0rLSkgNQoKKC3CtystKSA1">↗️</a><pre>    <span class='Paren'>(</span><span class='Function'>-+-</span><span class='Paren'>)</span> <span class='Number'>5</span>
@@ -15,8 +19,8 @@
     <span class='Paren'>(</span><span class='Function'>-</span><span class='Nothing'>·</span><span class='Function'>+-</span><span class='Paren'>)</span> <span class='Number'>5</span>
 5
 </pre>
-<h3 id="in-block-headers"><a class="header" href="#in-block-headers">In Block Headers</a></h3>
-<p>For Block header pattern matching syntax, Nothing can be used to indicate an unused value.</p>
+<h3 id="destructuring"><a class="header" href="#destructuring">Destructuring</a></h3>
+<p>For pattern matching in assignment or a block header, Nothing indicates an unused value.</p>
 <a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=RiDihpAge/CdlYogYeKAv8K34oC/YjogYeKIvmJ9CgpGIDHigL8y4oC/Mw==">↗️</a><pre>    <span class='Function'>F</span> <span class='Gets'>←</span> <span class='Brace'>{</span><span class='Function'>𝕊</span> <span class='Value'>a</span><span class='Ligature'>‿</span><span class='Nothing'>·</span><span class='Ligature'>‿</span><span class='Value'>b</span><span class='Head'>:</span> <span class='Value'>a</span><span class='Function'>∾</span><span class='Value'>b</span><span class='Brace'>}</span>
 
     <span class='Function'>F</span> <span class='Number'>1</span><span class='Ligature'>‿</span><span class='Number'>2</span><span class='Ligature'>‿</span><span class='Number'>3</span>
diff --git a/docs/help/rank.html b/docs/help/rank.html
index 1789d21f..e296e97a 100644
--- a/docs/help/rank.html
+++ b/docs/help/rank.html
@@ -6,7 +6,7 @@
 <div class="nav">(<a href="https://github.com/mlochbaum/BQN">github</a>) / <a href="../index.html">BQN</a> / <a href="index.html">help</a></div>
 <h1 id="circled-horizontal-bar-with-notch-"><a class="header" href="#circled-horizontal-bar-with-notch-">Circled Horizontal Bar With Notch (<code><span class='Modifier2'>⎉</span></code>)</a></h1>
 <h2 id="𝔽𝕘-𝕩-𝕨-𝔽𝕘-𝕩-rank"><a class="header" href="#𝔽𝕘-𝕩-𝕨-𝔽𝕘-𝕩-rank"><code><span class='Function'>𝔽</span><span class='Modifier2'>⎉</span><span class='Value'>𝕘</span> <span class='Value'>𝕩</span></code>, <code><span class='Value'>𝕨</span> <span class='Function'>𝔽</span><span class='Modifier2'>⎉</span><span class='Value'>𝕘</span> <span class='Value'>𝕩</span></code>: Rank</a></h2>
-<p>Apply <code><span class='Function'>𝔽</span></code> to cells at ranks given in <code><span class='Value'>𝕘</span></code>.</p>
+<p>Apply <code><span class='Function'>𝔽</span></code> to cells at ranks given in <code><span class='Value'>𝕘</span></code>. Non-negative numbers indicate the rank of the cell and negative ones indicate the difference from full rank.</p>
 <p>The ranks applied are given by the following:</p>
 <ul>
 <li><code><span class='Modifier2'>⎉</span> <span class='Value'>c</span></code>    Rank-c cells of <code><span class='Value'>𝕩</span></code> (monadic) or both arguments (dyadic)</li>
diff --git a/docs/help/rank_equals.html b/docs/help/rank_equals.html
index bd5b3727..65313deb 100644
--- a/docs/help/rank_equals.html
+++ b/docs/help/rank_equals.html
@@ -34,6 +34,7 @@
 </pre>
 <h2 id="𝕨--𝕩-equal-to"><a class="header" href="#𝕨--𝕩-equal-to"><code><span class='Value'>𝕨</span> <span class='Function'>=</span> <span class='Value'>𝕩</span></code>: Equal To</a></h2>
 <p><a class="fulldoc" href="../doc/arithmetic.html#comparisons">→full documentation</a></p>
+<p>Do argument atoms match?</p>
 <p><a href="../doc/arithmetic.html#pervasion">Pervasive.</a></p>
 <a class="replLink" title="Open in the REPL" target="_blank" href="https://mlochbaum.github.io/BQN/try.html#code=MSA9IDMKCjLigL8z4oC/MCA9IDPigL8x4oC/MAoKJ2EnID0gJ2En">↗️</a><pre>    <span class='Number'>1</span> <span class='Function'>=</span> <span class='Number'>3</span>
 0
diff --git a/help/depth.md b/help/depth.md
index 8c0d4367..bbe4d297 100644
--- a/help/depth.md
+++ b/help/depth.md
@@ -5,9 +5,11 @@
 ## `𝔽⚇𝕘 𝕩`, `𝕨 𝔽⚇𝕘 𝕩`: Depth
 [→full documentation](../doc/depth.md#the-depth-modifier)
 
-Apply `𝔽` to the cells of the arguments at depth given in `𝕘`.
+Apply `𝔽` to the cells of the arguments at depth given in `𝕘`. Negative numbers count down from the top level and non-negative ones from the bottom up.
 
 
         1⊸↓⚇1 ⟨⟨1,2,3⟩, ⟨4,5,6⟩⟩
 
         1 ↓⚇1 ⟨⟨1,2,3⟩, ⟨4,5,6⟩⟩
+
+        (+´↕)⚇0 ⟨2,4‿7,3⟩  # Implements pervasion
diff --git a/help/leftargument.md b/help/leftargument.md
index f8031f26..bda7fedc 100644
--- a/help/leftargument.md
+++ b/help/leftargument.md
@@ -8,3 +8,11 @@
 A variable assigned to the left argument of a block. `𝕎` can be used to access the left argument as a function.
 
         5 {𝕨} 1
+
+        -‿÷ {𝕎𝕩}¨ 4
+
+In a call with no left argument, `𝕨` functions as [Nothing](nothing.md) and `𝕎` can't be used.
+
+        {(-𝕨)⋈𝕩} 6
+
+        2 {(-𝕨)⋈𝕩} 6
diff --git a/help/length_notequals.md b/help/length_notequals.md
index 5d17237c..e13a14fe 100644
--- a/help/length_notequals.md
+++ b/help/length_notequals.md
@@ -23,6 +23,8 @@ Length of the first dimension of `𝕩`.
 ## `𝕨 ≠ 𝕩`: Not Equal To
 [→full documentation](../doc/arithmetic.md#comparisons)
 
+Do argument atoms not match?
+
 [Pervasive.](../doc/arithmetic.md#pervasion)
 
         1 ≠ 3
diff --git a/help/merge_greaterthan.md b/help/merge_greaterthan.md
index ee315fca..e78c063a 100644
--- a/help/merge_greaterthan.md
+++ b/help/merge_greaterthan.md
@@ -5,11 +5,9 @@
 ## `> 𝕩`: Merge
 [→full documentation](../doc/couple.md)
 
-Add the rank of an element of `𝕩` to the rank of `𝕩`.
+Combine an array of arrays into one array. All elements of `𝕩` must have the same rank, and the result rank is that plus the rank of `𝕩`.
 
-All elements must have the same rank.
-
-Returns atomic values as is.
+Returns and boxed atoms unchanged.
 
 
         a ← ⟨⟨1, 2⟩, ⟨3, 4⟩⟩
diff --git a/help/nothing.md b/help/nothing.md
index 0a5ad783..23aee6ba 100644
--- a/help/nothing.md
+++ b/help/nothing.md
@@ -5,6 +5,10 @@
 ## `·`: Nothing
 [→full documentation](../doc/expression.md#nothing)
 
+Indicates no value. If a left argument is Nothing, the function is called with no left argument, and if the right is Nothing, it's not called and "returns" Nothing.
+
+        · ⌽ "abc"  # Reverse instead of Rotate
+
 ### In Trains
 
 Nothing can serve as a left argument in a train to string together multiple monadic functions.
@@ -13,9 +17,9 @@ Nothing can serve as a left argument in a train to string together multiple mona
 
         (-·+-) 5
 
-### In Block Headers
+### Destructuring
 
-For Block header pattern matching syntax, Nothing can be used to indicate an unused value.
+For pattern matching in assignment or a block header, Nothing indicates an unused value.
 
         F ← {𝕊 a‿·‿b: a∾b}
 
diff --git a/help/rank.md b/help/rank.md
index 8f9e83ac..a3dddaf5 100644
--- a/help/rank.md
+++ b/help/rank.md
@@ -4,7 +4,7 @@
 
 ## `𝔽⎉𝕘 𝕩`, `𝕨 𝔽⎉𝕘 𝕩`: Rank
 
-Apply `𝔽` to cells at ranks given in `𝕘`.
+Apply `𝔽` to cells at ranks given in `𝕘`. Non-negative numbers indicate the rank of the cell and negative ones indicate the difference from full rank.
 
 The ranks applied are given by the following:
 
diff --git a/help/rank_equals.md b/help/rank_equals.md
index 0f41f6fa..ed590408 100644
--- a/help/rank_equals.md
+++ b/help/rank_equals.md
@@ -21,6 +21,8 @@ Returns the number of dimensions in `𝕩`.
 ## `𝕨 = 𝕩`: Equal To
 [→full documentation](../doc/arithmetic.md#comparisons)
 
+Do argument atoms match?
+
 [Pervasive.](../doc/arithmetic.md#pervasion)
 
         1 = 3