standard-classes.md

@@ -68,6 +68,13 @@ Proposals:
 
 Note that the `Float` and `Double` instances will not satisfy the usual axioms for these structures.
 
+### The Real class
+
+
+Issues:
+
+- The class assumes a mapping to `Rational`, but this cannot be defined for structures intermediate between the rationals and reals even though the operations of subclasses make sense for them, e.g. surds, computable reals.
+
 ### The Fractional class