TPTP Problem File: LCL181+1.p
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% File : LCL181+1 : TPTP v9.0.0. Released v2.0.0.
% Domain : Logic Calculi (Propositional)
% Problem : Principia Mathematica 2.15
% Version : Especial.
% English : Judged by [SRM73] to be the 'hardest' of the first 52 theorems
% of [WR27].
% Refs : [WR27] Whitehead & Russell (1927), Principia Mathematica
% : [SRM73] Siklossy et al. (1973), Breadth First Search: Some Sur
% : [Pel86] Pelletier (1986), Seventy-five Problems for Testing Au
% : [Hah94] Haehnle (1994), Email to G. Sutcliffe
% Source : [Hah94]
% Names : Pelletier 4 [Pel86]
% Status : Theorem
% Rating : 0.00 v2.5.0, 0.33 v2.4.0, 0.33 v2.2.1, 0.00 v2.1.0
% Syntax : Number of formulae : 1 ( 0 unt; 0 def)
% Number of atoms : 4 ( 0 equ)
% Maximal formula atoms : 4 ( 4 avg)
% Number of connectives : 5 ( 2 ~; 0 |; 0 &)
% ( 1 <=>; 2 =>; 0 <=; 0 <~>)
% Maximal formula depth : 4 ( 4 avg)
% Maximal term depth : 0 ( 0 avg)
% Number of predicates : 2 ( 2 usr; 2 prp; 0-0 aty)
% Number of functors : 0 ( 0 usr; 0 con; --- aty)
% Number of variables : 0 ( 0 !; 0 ?)
% SPC : FOF_THM_PRP
% Comments :
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fof(pel4,conjecture,
( ( ~ p
=> q )
<=> ( ~ q
=> p ) ) ).
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