## TPTP Problem File: SYN051-1.p

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```%--------------------------------------------------------------------------
% File     : SYN051-1 : TPTP v8.1.0. Released v1.0.0.
% Domain   : Syntactic
% Problem  : Pelletier Problem 21
% Version  : Especial.
% English  : A moderately tricky problem, especially for 'natural' systems
%            with 'strong' restrictions on variables generated from
%            existential quantifiers.

% Refs     : [Pel86] Pelletier (1986), Seventy-five Problems for Testing Au
% Source   : [Pel86]
% Names    : Pelletier 21 [Pel86]

% Status   : Unsatisfiable
% Rating   : 0.00 v2.0.0
% Syntax   : Number of clauses     :    4 (   0 unt;   1 nHn;   3 RR)
%            Number of literals    :    8 (   0 equ;   4 neg)
%            Maximal clause size   :    2 (   2 avg)
%            Maximal term depth    :    1 (   1 avg)
%            Number of predicates  :    2 (   2 usr;   1 prp; 0-1 aty)
%            Number of functors    :    2 (   2 usr;   2 con; 0-0 aty)
%            Number of variables   :    2 (   2 sgn)
% SPC      : CNF_UNS_EPR_NEQ_NHN

%--------------------------------------------------------------------------
cnf(clause_1,axiom,
( ~ p
| big_f(a) ) ).

cnf(clause_2,axiom,
( ~ big_f(b)
| p ) ).

cnf(clause_3,negated_conjecture,
( p
| big_f(X) ) ).

cnf(clause_4,negated_conjecture,
( ~ big_f(X)
| ~ p ) ).

%--------------------------------------------------------------------------
```