schwicht_n.002.ljt

%------------------------------------------------------------------------------
% File     : schwicht_n2 : Dyckhoff's benchmark formulae (1997)
% Domain   : Syntactic
% Problem  : Formulae with normal natural deduction proofs only of exponential size
% Version  : Especial.
%            Problem formulation : Inuit. Invalid.   Size 2
% English  : (~~p(N) & &&_{i=1..N} (p(i) => p(i) => p(i-1))) => p(0) 

% Refs     : [Dyc97] Roy Dyckhoff. Some benchmark formulae for
%                    intuitionistic propositional logic. At
%                    http://www.dcs.st-and.ac.uk/~rd/logic/marks.html
%          : [Sch97] H. Schwichtenberg, Termination of permutative
%                    conversions in Gentzen's sequent calculus,
%                    unpublished (1997). 
% Source   : [Dyc97]
% Names    : 

% Status   : Non-Theorem
% Rating   : 0.40 v 1.0
% Syntax   : Number of formulae    :    4 (   2 unit)
%            Number of atoms       :    8 (   0 equality)
%            Maximal formula depth :    3 (   2 average)
%            Number of connectives :    6 (   2 ~  ;   0  |;   0  &)
%                                         (   0 <=>;   4 =>;   0 <=)
%                                         (   0 <~>;   0 ~|;   0 ~&)
%            Number of predicates  :    3 (   3 propositional; 0-0 arity)
%            Number of functors    :    0 (   0 constant; --- arity)
%            Number of variables   :    0 (   0 singleton;   0 !;   0 ?)
%            Maximal term depth    :    0 (   0 average)

% Comments : "...no normal natural deduction proof of size less than an
%             expontial function of N.
%            ..Our experience of these problems is that they can be decided
%            very fast but can generate space problems, e.g. for some
%            implementations of Prolog." [Dyc97]
%          : tptp2X -f ljt schwicht_n.002.p 
%------------------------------------------------------------------------------

f((

% axiom1, axiom.
(( ~ ( ~ p2 ) ))

 & 

% axiom2, axiom.
(( p1 -> ( p1 -> p0 ) ))

 & 

% axiom3, axiom.
(( p2 -> ( p2 -> p1 ) ))

  ->

% conjecture_name, conjecture.
(p0)

)).

%------------------------------------------------------------------------------