%--------------------------------------------------------------------------
% File     : COL004-2 : TPTP v9.0.0. Bugfixed v2.3.0.
% Domain   : Combinatory Logic
% Problem  : Find combinator equivalent to U from S and K.
% Version  : [WM88] (equality) axioms.
%            Theorem formulation : The combination is provided and checked.
% English  : Construct from S and K alone a combinator that behaves as the
%            combinator U does, where ((Sx)y)z = (xz)(yz), (Kx)y = x,
%            (Ux)y = y((xx)y).

% Refs     : [WM88]  Wos & McCune (1988), Challenge Problems Focusing on Eq
% Source   : [TPTP]
% Names    :

% Status   : Unknown
% Rating   : 1.00 v2.0.0
% Syntax   :

% Comments :
% Bugfixes : v2.3.0 - Removed. The combinator, as given in [WM88] is wrong.
%            McCune says "Yes, there is a bug in that paper.  The combinator
%            ((s((s(ks))k))((s(k(s((s((sk)k))((sk)k)))))k)) is wrong. It is
%            not a typo error, so I can't correct it. I believe I could come
%            up with a replacement, but I don't think it's worth anything
%            for TPTP, because it will a trivial proof by rewriting (like
%            COL004-3 is). I suggest just throwing out problem COL004-2.
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