:- include(library(pfc_header_3_0)).

% -*-Prolog-*-


% if we learn that someone has a full name, then we know they are a user.
full_name(U,_) ==> user(U).


% if we learn that someone has a host name, then we know they are a user.
host_name(U,_) ==> user(U).


% when we know a user's full name and host name, make a user/3 assertion.
user(User),
full_name(User,Name),
host_name(User,Host) 
  ==>
  user(User,Name,Host).


% the default full_name for a user is 'unknown'.
user(User),
~full_name(User,X)/(X\==unknown)
  ==>
full_name(User,unknown).
  


% the default host_name for a user is 'unknown'.
user(User),
~host_name(User,X)/(X\==unknown)
  ==>
host_name(User,unknown).




==> full_name(finin,'Tim Finin').

==> host_name(finin,antares).

==> full_name(robin,'Robin,McEntire').

==> host_name(fritzson,hamlet).