Moved term ∅ to terms

Also add some codepoint information to some other terms

doc/Language/terms.pod6

@@ -163,8 +163,9 @@ Returns a pseudo-random L<Num|/type/Num> in the range C<0..^1>.
 
 =head2 term π
 
-Returns the number C<π>, i.e., the ratio between circumference and diameter
-of a circle. The ASCII equivalent of C<π> is C<pi>.
+Returns the number C<π> at codepoint U+03C0 (GREEK SMALL LETTER PI), i.e.
+the ratio between circumference and diameter of a circle. The ASCII equivalent
+of C<π> is C<pi>.
 
 =head2 term pi
 
@@ -173,17 +174,19 @@ of a circle. C<pi> is the ASCII equivalent of C<π>.
 
 =head2 term τ
 
-Returns the number C<τ>, i.e., the ratio between circumference and radius
-of a circle. The ASCII equivalent of C<τ> is C<tau>.
+Returns the number C<τ> at codepoint U+03C4 (GREEK SMALL LETTER TAU), i.e.
+the ratio between circumference and radius of a circle. The ASCII equivalent
+of C<τ> is C<tau>.
 
 =head2 term tau
 
-Returns the number C<τ>, i.e., the ratio between circumference and radius
-of a circle. C<tau> is the ASCII equivalent of C<τ>.
+Returns the number C<τ>, i.e.  the ratio between circumference and radius of
+a circle. C<tau> is the ASCII equivalent of C<τ>.
 
 =head2 term 𝑒
 
-Returns Euler's number.  The ASCII equivalent of C<𝑒> is C<e>.
+Returns Euler's number at codepoint U+1D452 (MATHEMATICAL ITALIC SMALL E).
+The ASCII equivalent of C<𝑒> is C<e>.
 
 =head2 term e
 
@@ -193,11 +196,18 @@ Returns Euler's number.  C<e> is the ASCII equivalent of C<𝑒>.
 
 Returns the imaginary unit (for L<Complex|/type/Complex> numbers).
 
+=head2 term ∅
+
+X<|∅>
+
+Returns C<set()>, aka the X<empty set>, at codepoint U+2205 (EMPTY SET).
+
 =head1 Variables
 
 Variables are discussed in the L<variable language docs |/language/variables>.
 
 X<|constant (Terms)>
+
 =head1 Constants
 
 Constants are similar to L<variables|/language/variables> without a