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 <h4 id="group">Group</h4>
 <p>I've been fiddling with the idea of function or map inversion (preimage creation, really) for several years, and in fact independently discovered something very similar to K's Group function <code><span class='Function'>=</span></code>, which is an excellent tool for languages that have dictionaries. I liked this approach as it didn't have all the ordering issues that J's Key has. However, I also didn't really want to introduce dictionaries to BQN, as they have a very strange relation to multidimensional arrays—are arrays like dictionaries with multiple keys, or dictionaries with a single vector key? I've been a proponent of <code><span class='Function'>/</span><span class='Modifier'>⁼</span></code> as a programming tool for <a href="http://www.jsoftware.com/pipermail/programming/2010-September/020302.html">much longer</a>. I'd also developed a sophisticated view of <a href="https://aplwiki.com/wiki/Partition_representations">partition representations</a> while studying an extension to Dyalog's Partitioned Enclose proposed by Adám and included in Dyalog 18.0. I finally put all this together while fighting with Key to develop BQN's compiler: I realized that if the &quot;key&quot; argument was restricted to array indices, then it would make sense for the result to be an array, and that this was simply the &quot;target indices&quot; partition representation minus the requirement that those indices be nondecreasing.</p>
 <h4 id="before--and-after-">Before <code><span class='Modifier2'>⊸</span></code> and After <code><span class='Modifier2'>⟜</span></code></h4>
-<p>It happens that BQN's Before (<code><span class='Modifier2'>⊸</span></code>) and After (<code><span class='Modifier2'>⟜</span></code>) modifiers are identical to I's hook (<code><span class='Value'>h</span></code>) and backhook (<code><span class='Function'>H</span></code>), but it took some time to arrive at this point. The hook function in I comes from J's 2-train, also called hook. But the model for Before and After was initially APL's Compose (∘) and the complement <a href="https://aplwiki.com/wiki/Reverse_Compose">Reverse Compose</a> that Adám created for Extended Dyalog APL. I noticed the similarity to Bind and decided to unify Binds and Composes at around the same time that I picked the symbols <code><span class='Modifier2'>⊸⟜</span></code>. However, I kept the idea that the one-argument case should be simple composition unless the bound operand had a subject role. Eventually I decided the violation of <a href="../problems.html#syntactic-type-erasure">syntactic type erasure</a> was too inconsistent and settled on the current definition. Now I think these forms are better even ignoring constant functions, although I do occasionally run into cases where I'd like to use APL's Compose.</p>
+<p>It happens that BQN's Before (<code><span class='Modifier2'>⊸</span></code>) and After (<code><span class='Modifier2'>⟜</span></code>) modifiers are identical to I's hook (<code><span class='Value'>h</span></code>) and backhook (<code><span class='Function'>H</span></code>), but it took some time to arrive at this point. The hook function in I comes from J's 2-train, also called hook. But the model for Before and After was initially APL's Compose (∘) and the complement <a href="https://aplwiki.com/wiki/Reverse_Compose">Reverse Compose</a> that Adám created for Extended Dyalog APL. I noticed the similarity to Bind and decided to unify Binds and Composes at around the same time that I picked the symbols <code><span class='Modifier2'>⊸⟜</span></code>. However, I kept the idea that the one-argument case should be simple composition unless the bound operand had a subject role. Eventually I decided the violation of <a href="problems.html#syntactic-type-erasure">syntactic type erasure</a> was too inconsistent and settled on the current definition. Now I think these forms are better even ignoring constant functions, although I do occasionally run into cases where I'd like to use APL's Compose.</p>
 <h4 id="constant-modifier">Constant modifier</h4>
 <p>The idea of a constant function is nothing new; I named it <code><span class='Value'>k</span></code> in I, taking influence from the <a href="https://en.wikipedia.org/wiki/SKI_combinator_calculus">SKI</a> calculus. It was actually Adám who suggested adding it to Dyalog with the glyph <code><span class='Value'>⍨</span></code>, although I was the one who campaigned for it and introduced it to the public in version 18.0. It wasn't initially clear that a dedicated modifier was needed in BQN because the treatment of data types as constant functions seems to fill this role, but I eventually found that I needed a constant function returning a function too often to leave it out.</p>