Specify more •math functions and implement JS Fact, Comb, GCD, LCM

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 <p>It's not hard to prove that the bilinear extensions have these identity values. Of course <code><span class='Number'>1</span><span class='Function'>∧</span><span class='Value'>x</span></code> is <code><span class='Number'>1</span><span class='Function'>×</span><span class='Value'>x</span></code>, or <code><span class='Value'>x</span></code>, and <code><span class='Number'>0</span><span class='Function'>∨</span><span class='Value'>x</span></code> is <code><span class='Number'>0</span><span class='Function'>×</span><span class='Modifier2'>⌾</span><span class='Function'>¬</span><span class='Value'>x</span></code>, or <code><span class='Function'>¬</span><span class='Number'>1</span><span class='Function'>׬</span><span class='Value'>x</span></code>, giving <code><span class='Function'>¬¬</span><span class='Value'>x</span></code> or <code><span class='Value'>x</span></code> again. Both functions are commutative, so these values are identities on the right as well.</p>
 <p>Some other logical identities don't always hold. For example, in boolean logic And distributes over Or and vice-versa: <code><span class='Value'>a</span><span class='Function'>∧</span><span class='Value'>b</span><span class='Function'>∨</span><span class='Value'>c</span> <span class='Gets'>←→</span> <span class='Paren'>(</span><span class='Value'>a</span><span class='Function'>∧</span><span class='Value'>b</span><span class='Paren'>)</span><span class='Function'>∨</span><span class='Paren'>(</span><span class='Value'>a</span><span class='Function'>∧</span><span class='Value'>c</span><span class='Paren'>)</span></code>. But substituting <code><span class='Function'>×</span></code> for <code><span class='Function'>∧</span></code> and <code><span class='Function'>+-×</span></code> for <code><span class='Function'>∨</span></code> we find that the left hand side is <code><span class='Paren'>(</span><span class='Value'>a</span><span class='Function'>×</span><span class='Value'>b</span><span class='Paren'>)</span><span class='Function'>+</span><span class='Paren'>(</span><span class='Value'>a</span><span class='Function'>×</span><span class='Value'>c</span><span class='Paren'>)</span><span class='Function'>+</span><span class='Paren'>(</span><span class='Value'>a</span><span class='Function'>×</span><span class='Value'>b</span><span class='Function'>×</span><span class='Value'>c</span><span class='Paren'>)</span></code> while the right gives <code><span class='Paren'>(</span><span class='Value'>a</span><span class='Function'>×</span><span class='Value'>b</span><span class='Paren'>)</span><span class='Function'>+</span><span class='Paren'>(</span><span class='Value'>a</span><span class='Function'>×</span><span class='Value'>c</span><span class='Paren'>)</span><span class='Function'>+</span><span class='Paren'>(</span><span class='Value'>a</span><span class='Function'>×</span><span class='Value'>b</span><span class='Function'>×</span><span class='Value'>a</span><span class='Function'>×</span><span class='Value'>c</span><span class='Paren'>)</span></code>. These are equivalent for arbitrary <code><span class='Value'>b</span></code> and <code><span class='Value'>c</span></code> only if <code><span class='Value'>a</span><span class='Function'>=</span><span class='Value'>a</span><span class='Function'>×</span><span class='Value'>a</span></code>, that is, <code><span class='Value'>a</span></code> is 0 or 1. In terms of probabilities the difference when <code><span class='Value'>a</span></code> is not boolean is caused by failure of independence. On the left hand side, the two arguments of every logical function are independent. On the right hand side, each pair of arguments to <code><span class='Function'>∧</span></code> are independent, but the two arguments to <code><span class='Function'>∨</span></code>, <code><span class='Value'>a</span><span class='Function'>∧</span><span class='Value'>b</span></code> and <code><span class='Value'>a</span><span class='Function'>∧</span><span class='Value'>c</span></code>, are not. The relationship between these arguments means that logical equivalences no longer apply.</p>
 <h3 id="why-not-gcd-and-lcm"><a class="header" href="#why-not-gcd-and-lcm">Why not GCD and LCM?</a></h3>
-<p>APL provides <a href="https://aplwiki.com/wiki/GCD">GCD</a> and <a href="https://aplwiki.com/wiki/LCM">LCM</a> as extensions of And and Or, while BQN doesn't make these functions primitives. The main reason for omitting them functions is that they are complicated and, when applied to real or complex numbers, require a significant number of design decisions where there's no obvious choice (for example, whether to use comparison tolerance). On the other hand, these functions are fairly easy to implement, which allows the programmer to control the details, and also add functionality such as the extended GCD. Possible implementations for GCD and LCM are shown in <a href="https://mlochbaum.github.io/bqncrate">bqncrate</a> (<a href="https://mlochbaum.github.io/bqncrate/?q=gcd">GCD</a>, <a href="https://mlochbaum.github.io/bqncrate/?q=lcm">LCM</a>).</p>
+<p>APL provides <a href="https://aplwiki.com/wiki/GCD">GCD</a> and <a href="https://aplwiki.com/wiki/LCM">LCM</a> as extensions of And and Or, while BQN doesn't make these functions primitives. The main reason for omitting them functions is that they are complicated and, when applied to real or complex numbers, require a significant number of design decisions where there's no obvious choice (for example, whether to use comparison tolerance). On the other hand, these functions are fairly easy to implement, which allows the programmer to control the details, and also add functionality such as the extended GCD. Possible implementations for GCD and LCM are shown in <a href="https://mlochbaum.github.io/bqncrate">bqncrate</a> (<a href="https://mlochbaum.github.io/bqncrate/?q=gcd">GCD</a>, <a href="https://mlochbaum.github.io/bqncrate/?q=lcm">LCM</a>), and <code><span class='Value'>•math.</span><span class='Function'>GCD</span></code> and <code><span class='Value'>•math.</span><span class='Function'>LCM</span></code> are also supported.</p>
 <p>A secondary reason is that the GCD falls short as an extension of Or, because its identity value 0 is not total. <code><span class='Number'>0</span><span class='Function'>∨</span><span class='Value'>x</span></code>, for a real number <code><span class='Value'>x</span></code>, is actually equal to <code><span class='Function'>|</span><span class='Value'>x</span></code> and not <code><span class='Value'>x</span></code>: for example, <code><span class='Number'>0</span><span class='Function'>∨</span><span class='Number'>¯2</span></code> is <code><span class='Number'>2</span></code> in APL. This means the identity <code><span class='Number'>0</span><span class='Function'>∨</span><span class='Value'>x</span> <span class='Gets'>←→</span> <span class='Value'>x</span></code> isn't reliable in APL.</p>
 <p>Unrelatedly, the reason BQN discards APL's <code><span class='Value'>~</span></code> for negation is that it looks like <code><span class='Modifier'>˜</span></code>, and is less common in mathematics today.</p>