## TPTP Problem File: PUZ004-1.p

View Solutions
- Solve Problem

%--------------------------------------------------------------------------
% File : PUZ004-1 : TPTP v8.1.0. Released v1.0.0.
% Domain : Puzzles
% Problem : The Letters Puzzle
% Version : Especial.
% English : (1) All the dated letters in this room are written on blue paper.
% (2) None of them are in black ink except those that are written
% in the third person.
% (3) I have not filed any of them that I can read.
% (4) None of them that are written on one sheet are undated.
% (5) All of them that are not crossed are in black ink. :
% (6) All of them written by Brown begin with "Dear Sir" :
% (7) All of them written on blue paper are filed. :
% (8) None of them written on more than one sheet are crossed.
% (9) None of them that begin with "Dear Sir" are written
% in third person.
% Prove that letters by Brown cannot be read.
% Refs : [Car86] Carroll (1986), Lewis Carroll's Symbolic Logic
% Source : [ANL]
% Names : letters.ver1.in [ANL]
% Status : Unsatisfiable
% Rating : 0.00 v2.0.0
% Syntax : Number of clauses : 12 ( 2 unt; 1 nHn; 12 RR)
% Number of literals : 22 ( 0 equ; 11 neg)
% Maximal clause size : 2 ( 1 avg)
% Maximal term depth : 0 ( 0 avg)
% Number of predicates : 10 ( 10 usr; 10 prp; 0-0 aty)
% Number of functors : 0 ( 0 usr; 0 con; --- aty)
% Number of variables : 0 ( 0 sgn)
% SPC : CNF_UNS_PRP
% Comments :
%--------------------------------------------------------------------------
cnf(dated_on_blue_paper,axiom,
( ~ dated
| on_blue_paper ) ).
cnf(third_person_in_black_ink,axiom,
( ~ in_third_person
| in_black_ink ) ).
cnf(black_ink_in_third_person,axiom,
( in_third_person
| ~ in_black_ink ) ).
cnf(not_filed_if_read,axiom,
( ~ can_be_read
| ~ filed ) ).
cnf(dated_if_on_one_sheet,axiom,
( ~ on_one_sheet
| dated ) ).
cnf(not_crossed_in_black_ink,axiom,
( crossed
| in_black_ink ) ).
cnf(brown_starts_with_sir,axiom,
( ~ by_brown
| begins_with_dear_sir ) ).
cnf(filed_if_on_blue_paper,axiom,
( ~ on_blue_paper
| filed ) ).
cnf(on_one_sheet_if_crossed,axiom,
( on_one_sheet
| ~ crossed ) ).
cnf(no_dear_sirs_in_third_person,axiom,
( ~ begins_with_dear_sir
| ~ in_third_person ) ).
cnf(letter_by_brown,hypothesis,
by_brown ).
cnf(prove_it_cannot_be_read,negated_conjecture,
can_be_read ).
%--------------------------------------------------------------------------