Here is the Prolog program given by Mostowski Collapse https://stackoverflow.com/users/502187/mostowski-collapseMostowski Collapse at the Stackoverflow webpage that I mentioned at the beginning of this post. I only changed the disjunction operator ! for ’ | ’ :

```
% operator definitions (TPTP syntax)
:- op( 500, fy, ~). % negation
:- op(1000, xfy, &). % conjunction
:- op(1100, xfy, '|'). % disjunction
% :- op(1110, xfy, =>). % implication
% :- op(1110, xfy, <=>). % biconditional
eval(A, A) :- var(A), !.
eval(A&B, R) :- !, eval(A, X), eval(B, Y), simp(X&Y, R).
eval(A '|' B, R) :- !, eval(A, X), eval(B, Y), simp(X '|' Y, R).
eval(~A, R) :- !, eval(A, X), simp(~X, R).
eval(A, A).
simp(A, A) :- var(A), !.
simp(A&_, 0) :- A == 0, !.
simp(_&B, 0) :- B == 0, !.
simp(A&B, B) :- A == 1, !.
simp(A&B, A) :- B == 1, !.
simp(A '|' B, B) :- A == 0, !.
simp(A '|' B, A) :- B == 0, !.
simp(A '|'_, 1) :- A == 1, !.
simp(_ '|' B, 1) :- B == 1, !.
simp(~A, 1) :- A == 0, !.
simp(~A, 0) :- A == 1, !.
simp(A, A).
unsat(A) :- eval(A, B), term_variables(B, L), unsat(B, L).
unsat(0, _) :- !.
unsat(A, [0|_]) :- unsat(A), !.
unsat(A, [1|_]) :- unsat(A).
```

This prover is able to find quickly a counter-model for the following big disjunctive formula:

```
?- unsat((( A11 & A21 ) | ( ( A11 & A31 ) | ( ( A11 & A41 ) | ( ( A11 & A51 ) | ( ( A11 & A61 ) | ( ( A21 & A31 ) | ( ( A21 & A41 ) | ( ( A21 & A51 ) | ( ( A21 & A61 ) | ( ( A31 & A41 ) | ( ( A31 & A51 ) | ( ( A31 & A61 ) | ( ( A41 & A51 ) | ( ( A41 & A61 ) | ( ( A51 & A61 ) | ( ( A12 & A22 ) | ( ( A12 & A32 ) | ( ( A12 & A42 ) | ( ( A12 & A52 ) | ( ( A12 & A62 ) | ( ( A22 & A32 ) | ( ( A22 & A42 ) | ( ( A22 & A52 ) | ( ( A22 & A62 ) | ( ( A32 & A42 ) | ( ( A32 & A52 ) | ( ( A32 & A62 ) | ( ( A42 & A52 ) | ( ( A42 & A62 ) | ( ( A52 & A62 ) | ( ( A13 & A23 ) | ( ( A13 & A33 ) | ( ( A13 & A43 ) | ( ( A13 & A53 ) | ( ( A13 & A63 ) | ( ( A23 & A33 ) | ( ( A23 & A43 ) | ( ( A23 & A53 ) | ( ( A23 & A63 ) | ( ( A33 & A43 ) | ( ( A33 & A53 ) | ( ( A33 & A63 ) | ( ( A43 & A53 ) | ( ( A43 & A63 ) | ( ( A53 & A63 ) | ( ( A14 & A24 ) | ( ( A14 & A34 ) | ( ( A14 & A44 ) | ( ( A14 & A54 ) | ( ( A14 & A64 ) | ( ( A24 & A34 ) | ( ( A24 & A44 ) | ( ( A24 & A54 ) | ( ( A24 & A64 ) | ( ( A34 & A44 ) | ( ( A34 & A54 ) | ( ( A34 & A64 ) | ( ( A44 & A54 ) | ( ( A44 & A64 ) | ( ( A54 & A64 ) | ( ( A15 & A25 ) | ( ( A15 & A35 ) | ( ( A15 & A45 ) | ( ( A15 & A55 ) | ( ( A15 & A65 ) | ( ( A25 & A35 ) | ( ( A25 & A45 ) | ( ( A25 & A55 ) | ( ( A25 & A65 ) | ( ( A35 & A45 ) | ( ( A35 & A55 ) | ( ( A35 & A65 ) | ( ( A45 & A55 ) | ( ( A45 & A65 ) | ( A55 & A65 ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) )).
A11 = A21, A21 = A31, A31 = A41, A41 = A51, A51 = A12, A12 = A22, A22 = A32, A32 = A42, A42 = A52, A52 = A13, A13 = A23, A23 = A33, A33 = A43, A43 = A53, A53 = A14, A14 = A24, A24 = A34, A34 = A44, A44 = A54, A54 = A15, A15 = A25, A25 = A35, A35 = A45, A45 = A55, A55 = 0.
```