~~~~~~~o~~~~~~~~~o~~~~~~~~~o~~~~~~~~~o~~~~~~~~~o

| 4.  Semantical Rules (cont.)
|
| It may be instructive to compare the notion of semantical rule with that
| of postulate.  Relative to a given set of postulates, it is easy to say
| what a postulate is:  it is a member of the set.  Relative to a given
| set of semantical rules, it is equally easy to say what a semantical
| rule is.  But given simply a notation, mathematical or otherwise,
| and indeed as thoroughly understood a notation as you please in
| p