If a construct which uses a system or user-defined external function
is loaded before a generic function which uses that function as
an implicit method, all calls to that function from
that construct will bypass the generic dispatch.
For example, if a generic function which overloads the "+"
operator is defined after a rule which uses the "+"
operator, that rule will always call the "+" system
function directly. However, similar rules defined after the generic
function will use the generic dispatch.