/// There is a TypeMap typedef that is the mapping of names to Types.
/// Similarly there is a ValueMap typedef that is the mapping of
/// names to Values. Finally, there is a PlaneMap typedef that is the
-/// mapping of types to planes of ValueMap. THis is the basic structure
+/// mapping of types to planes of ValueMap. This is the basic structure
/// of the symbol table. When you call type_begin() you're asking
/// for an iterator at the start of the TypeMap. When you call
/// plane_begin(), you're asking for an iterator at the start of