author | paulson |
Thu, 10 Feb 2000 11:08:42 +0100 | |
changeset 8226 | 07284f7ad262 |
parent 6799 | 95abcc002a21 |
child 10212 | 33fe2d701ddd |
permissions | -rw-r--r-- |
1465 | 1 |
(* Title: HOL/ex/cla |
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ID: $Id$ |
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Author: Lawrence C Paulson, Cambridge University Computer Laboratory |
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Copyright 1994 University of Cambridge |
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Higher-Order Logic: predicate calculus problems |
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Taken from FOL/cla.ML; beware of precedence of = vs <-> |
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*) |
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writeln"File HOL/ex/cla."; |
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||
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context HOL.thy; |
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Goal "(P --> Q | R) --> (P-->Q) | (P-->R)"; |
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by (Blast_tac 1); |
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result(); |
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(*If and only if*) |
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||
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Goal "(P=Q) = (Q = (P::bool))"; |
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by (Blast_tac 1); |
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result(); |
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||
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Goal "~ (P = (~P))"; |
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by (Blast_tac 1); |
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result(); |
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(*Sample problems from |
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F. J. Pelletier, |
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Seventy-Five Problems for Testing Automatic Theorem Provers, |
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J. Automated Reasoning 2 (1986), 191-216. |
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Errata, JAR 4 (1988), 236-236. |
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The hardest problems -- judging by experience with several theorem provers, |
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including matrix ones -- are 34 and 43. |
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*) |
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writeln"Pelletier's examples"; |
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(*1*) |
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Goal "(P-->Q) = (~Q --> ~P)"; |
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by (Blast_tac 1); |
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result(); |
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(*2*) |
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Goal "(~ ~ P) = P"; |
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by (Blast_tac 1); |
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result(); |
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(*3*) |
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Goal "~(P-->Q) --> (Q-->P)"; |
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by (Blast_tac 1); |
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result(); |
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(*4*) |
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Goal "(~P-->Q) = (~Q --> P)"; |
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by (Blast_tac 1); |
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result(); |
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(*5*) |
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Goal "((P|Q)-->(P|R)) --> (P|(Q-->R))"; |
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by (Blast_tac 1); |
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result(); |
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(*6*) |
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Goal "P | ~ P"; |
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by (Blast_tac 1); |
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result(); |
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(*7*) |
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Goal "P | ~ ~ ~ P"; |
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by (Blast_tac 1); |
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result(); |
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(*8. Peirce's law*) |
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Goal "((P-->Q) --> P) --> P"; |
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by (Blast_tac 1); |
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result(); |
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(*9*) |
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Goal "((P|Q) & (~P|Q) & (P| ~Q)) --> ~ (~P | ~Q)"; |
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by (Blast_tac 1); |
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result(); |
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(*10*) |
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Goal "(Q-->R) & (R-->P&Q) & (P-->Q|R) --> (P=Q)"; |
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by (Blast_tac 1); |
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result(); |
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(*11. Proved in each direction (incorrectly, says Pelletier!!) *) |
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Goal "P=(P::bool)"; |
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by (Blast_tac 1); |
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result(); |
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(*12. "Dijkstra's law"*) |
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Goal "((P = Q) = R) = (P = (Q = R))"; |
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by (Blast_tac 1); |
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result(); |
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(*13. Distributive law*) |
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Goal "(P | (Q & R)) = ((P | Q) & (P | R))"; |
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by (Blast_tac 1); |
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result(); |
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(*14*) |
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Goal "(P = Q) = ((Q | ~P) & (~Q|P))"; |
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by (Blast_tac 1); |
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result(); |
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(*15*) |
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Goal "(P --> Q) = (~P | Q)"; |
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by (Blast_tac 1); |
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result(); |
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(*16*) |
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Goal "(P-->Q) | (Q-->P)"; |
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by (Blast_tac 1); |
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result(); |
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(*17*) |
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Goal "((P & (Q-->R))-->S) = ((~P | Q | S) & (~P | ~R | S))"; |
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by (Blast_tac 1); |
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result(); |
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writeln"Classical Logic: examples with quantifiers"; |
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Goal "(! x. P(x) & Q(x)) = ((! x. P(x)) & (! x. Q(x)))"; |
2891 | 129 |
by (Blast_tac 1); |
969 | 130 |
result(); |
131 |
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Goal "(? x. P-->Q(x)) = (P --> (? x. Q(x)))"; |
2891 | 133 |
by (Blast_tac 1); |
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result(); |
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Goal "(? x. P(x)-->Q) = ((! x. P(x)) --> Q)"; |
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by (Blast_tac 1); |
969 | 138 |
result(); |
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Goal "((! x. P(x)) | Q) = (! x. P(x) | Q)"; |
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by (Blast_tac 1); |
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result(); |
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144 |
(*From Wishnu Prasetya*) |
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Goal "(!s. q(s) --> r(s)) & ~r(s) & (!s. ~r(s) & ~q(s) --> p(t) | q(t)) \ |
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\ --> p(t) | r(t)"; |
2891 | 147 |
by (Blast_tac 1); |
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result(); |
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150 |
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writeln"Problems requiring quantifier duplication"; |
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(*Theorem B of Peter Andrews, Theorem Proving via General Matings, |
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JACM 28 (1981).*) |
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Goal "(EX x. ALL y. P(x) = P(y)) --> ((EX x. P(x)) = (ALL y. P(y)))"; |
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by (Blast_tac 1); |
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result(); |
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(*Needs multiple instantiation of the quantifier.*) |
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Goal "(! x. P(x)-->P(f(x))) & P(d)-->P(f(f(f(d))))"; |
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by (Blast_tac 1); |
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result(); |
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(*Needs double instantiation of the quantifier*) |
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Goal "? x. P(x) --> P(a) & P(b)"; |
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by (Blast_tac 1); |
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result(); |
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Goal "? z. P(z) --> (! x. P(x))"; |
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by (Blast_tac 1); |
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result(); |
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Goal "? x. (? y. P(y)) --> P(x)"; |
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by (Blast_tac 1); |
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result(); |
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writeln"Hard examples with quantifiers"; |
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writeln"Problem 18"; |
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Goal "? y. ! x. P(y)-->P(x)"; |
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by (Blast_tac 1); |
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result(); |
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writeln"Problem 19"; |
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Goal "? x. ! y z. (P(y)-->Q(z)) --> (P(x)-->Q(x))"; |
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by (Blast_tac 1); |
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result(); |
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writeln"Problem 20"; |
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Goal "(! x y. ? z. ! w. (P(x)&Q(y)-->R(z)&S(w))) \ |
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\ --> (? x y. P(x) & Q(y)) --> (? z. R(z))"; |
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by (Blast_tac 1); |
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result(); |
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writeln"Problem 21"; |
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Goal "(? x. P-->Q(x)) & (? x. Q(x)-->P) --> (? x. P=Q(x))"; |
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by (Blast_tac 1); |
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result(); |
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writeln"Problem 22"; |
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Goal "(! x. P = Q(x)) --> (P = (! x. Q(x)))"; |
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by (Blast_tac 1); |
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result(); |
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writeln"Problem 23"; |
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Goal "(! x. P | Q(x)) = (P | (! x. Q(x)))"; |
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by (Blast_tac 1); |
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result(); |
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writeln"Problem 24"; |
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Goal "~(? x. S(x)&Q(x)) & (! x. P(x) --> Q(x)|R(x)) & \ |
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\ (~(? x. P(x)) --> (? x. Q(x))) & (! x. Q(x)|R(x) --> S(x)) \ |
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\ --> (? x. P(x)&R(x))"; |
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by (Blast_tac 1); |
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result(); |
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writeln"Problem 25"; |
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Goal "(? x. P(x)) & \ |
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\ (! x. L(x) --> ~ (M(x) & R(x))) & \ |
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\ (! x. P(x) --> (M(x) & L(x))) & \ |
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\ ((! x. P(x)-->Q(x)) | (? x. P(x)&R(x))) \ |
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\ --> (? x. Q(x)&P(x))"; |
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2891 | 223 |
by (Blast_tac 1); |
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result(); |
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writeln"Problem 26"; |
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Goal "((? x. p(x)) = (? x. q(x))) & \ |
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\ (! x. ! y. p(x) & q(y) --> (r(x) = s(y))) \ |
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\ --> ((! x. p(x)-->r(x)) = (! x. q(x)-->s(x)))"; |
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by (Blast_tac 1); |
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result(); |
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writeln"Problem 27"; |
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Goal "(? x. P(x) & ~Q(x)) & \ |
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\ (! x. P(x) --> R(x)) & \ |
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\ (! x. M(x) & L(x) --> P(x)) & \ |
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\ ((? x. R(x) & ~ Q(x)) --> (! x. L(x) --> ~ R(x))) \ |
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\ --> (! x. M(x) --> ~L(x))"; |
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by (Blast_tac 1); |
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result(); |
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writeln"Problem 28. AMENDED"; |
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Goal "(! x. P(x) --> (! x. Q(x))) & \ |
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\ ((! x. Q(x)|R(x)) --> (? x. Q(x)&S(x))) & \ |
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\ ((? x. S(x)) --> (! x. L(x) --> M(x))) \ |
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\ --> (! x. P(x) & L(x) --> M(x))"; |
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by (Blast_tac 1); |
969 | 248 |
result(); |
249 |
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writeln"Problem 29. Essentially the same as Principia Mathematica *11.71"; |
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Goal "(? x. F(x)) & (? y. G(y)) \ |
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\ --> ( ((! x. F(x)-->H(x)) & (! y. G(y)-->J(y))) = \ |
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\ (! x y. F(x) & G(y) --> H(x) & J(y)))"; |
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2891 | 254 |
by (Blast_tac 1); |
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result(); |
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writeln"Problem 30"; |
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Goal "(! x. P(x) | Q(x) --> ~ R(x)) & \ |
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\ (! x. (Q(x) --> ~ S(x)) --> P(x) & R(x)) \ |
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\ --> (! x. S(x))"; |
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by (Blast_tac 1); |
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result(); |
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writeln"Problem 31"; |
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Goal "~(? x. P(x) & (Q(x) | R(x))) & \ |
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\ (? x. L(x) & P(x)) & \ |
267 |
\ (! x. ~ R(x) --> M(x)) \ |
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\ --> (? x. L(x) & M(x))"; |
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2891 | 269 |
by (Blast_tac 1); |
969 | 270 |
result(); |
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writeln"Problem 32"; |
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Goal "(! x. P(x) & (Q(x)|R(x))-->S(x)) & \ |
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\ (! x. S(x) & R(x) --> L(x)) & \ |
275 |
\ (! x. M(x) --> R(x)) \ |
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\ --> (! x. P(x) & M(x) --> L(x))"; |
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2891 | 277 |
by (Blast_tac 1); |
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result(); |
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writeln"Problem 33"; |
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Goal "(! x. P(a) & (P(x)-->P(b))-->P(c)) = \ |
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\ (! x. (~P(a) | P(x) | P(c)) & (~P(a) | ~P(b) | P(c)))"; |
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by (Blast_tac 1); |
969 | 284 |
result(); |
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||
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writeln"Problem 34 AMENDED (TWICE!!)"; |
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(*Andrews's challenge*) |
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Goal "((? x. ! y. p(x) = p(y)) = \ |
3019 | 289 |
\ ((? x. q(x)) = (! y. p(y)))) = \ |
290 |
\ ((? x. ! y. q(x) = q(y)) = \ |
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\ ((? x. p(x)) = (! y. q(y))))"; |
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2891 | 292 |
by (Blast_tac 1); |
969 | 293 |
result(); |
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writeln"Problem 35"; |
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Goal "? x y. P x y --> (! u v. P u v)"; |
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by (Blast_tac 1); |
969 | 298 |
result(); |
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writeln"Problem 36"; |
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Goal "(! x. ? y. J x y) & \ |
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\ (! x. ? y. G x y) & \ |
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\ (! x y. J x y | G x y --> \ |
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\ (! z. J y z | G y z --> H x z)) \ |
305 |
\ --> (! x. ? y. H x y)"; |
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2891 | 306 |
by (Blast_tac 1); |
969 | 307 |
result(); |
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writeln"Problem 37"; |
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5150 | 310 |
Goal "(! z. ? w. ! x. ? y. \ |
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\ (P x z -->P y w) & P y z & (P y w --> (? u. Q u w))) & \ |
969 | 312 |
\ (! x z. ~(P x z) --> (? y. Q y z)) & \ |
313 |
\ ((? x y. Q x y) --> (! x. R x x)) \ |
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\ --> (! x. ? y. R x y)"; |
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2891 | 315 |
by (Blast_tac 1); |
969 | 316 |
result(); |
317 |
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writeln"Problem 38"; |
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Goal "(! x. p(a) & (p(x) --> (? y. p(y) & r x y)) --> \ |
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\ (? z. ? w. p(z) & r x w & r w z)) = \ |
321 |
\ (! x. (~p(a) | p(x) | (? z. ? w. p(z) & r x w & r w z)) & \ |
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1716
8dbf9ca61ce5
Restored a proof of Pelletier #38 -- mysteriously deleted
paulson
parents:
1712
diff
changeset
|
322 |
\ (~p(a) | ~(? y. p(y) & r x y) | \ |
969 | 323 |
\ (? z. ? w. p(z) & r x w & r w z)))"; |
2891 | 324 |
by (Blast_tac 1); (*beats fast_tac!*) |
1716
8dbf9ca61ce5
Restored a proof of Pelletier #38 -- mysteriously deleted
paulson
parents:
1712
diff
changeset
|
325 |
result(); |
969 | 326 |
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327 |
writeln"Problem 39"; |
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5150 | 328 |
Goal "~ (? x. ! y. F y x = (~ F y y))"; |
2891 | 329 |
by (Blast_tac 1); |
969 | 330 |
result(); |
331 |
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332 |
writeln"Problem 40. AMENDED"; |
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5150 | 333 |
Goal "(? y. ! x. F x y = F x x) \ |
969 | 334 |
\ --> ~ (! x. ? y. ! z. F z y = (~ F z x))"; |
2891 | 335 |
by (Blast_tac 1); |
969 | 336 |
result(); |
337 |
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338 |
writeln"Problem 41"; |
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5150 | 339 |
Goal "(! z. ? y. ! x. f x y = (f x z & ~ f x x)) \ |
969 | 340 |
\ --> ~ (? z. ! x. f x z)"; |
2891 | 341 |
by (Blast_tac 1); |
969 | 342 |
result(); |
343 |
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344 |
writeln"Problem 42"; |
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5150 | 345 |
Goal "~ (? y. ! x. p x y = (~ (? z. p x z & p z x)))"; |
2891 | 346 |
by (Blast_tac 1); |
969 | 347 |
result(); |
348 |
||
2891 | 349 |
writeln"Problem 43!!"; |
5278 | 350 |
Goal "(! x::'a. ! y::'a. q x y = (! z. p z x = (p z y::bool))) \ |
969 | 351 |
\ --> (! x. (! y. q x y = (q y x::bool)))"; |
2891 | 352 |
by (Blast_tac 1); |
3347 | 353 |
result(); |
969 | 354 |
|
355 |
writeln"Problem 44"; |
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5150 | 356 |
Goal "(! x. f(x) --> \ |
969 | 357 |
\ (? y. g(y) & h x y & (? y. g(y) & ~ h x y))) & \ |
1465 | 358 |
\ (? x. j(x) & (! y. g(y) --> h x y)) \ |
969 | 359 |
\ --> (? x. j(x) & ~f(x))"; |
2891 | 360 |
by (Blast_tac 1); |
969 | 361 |
result(); |
362 |
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363 |
writeln"Problem 45"; |
|
5278 | 364 |
Goal "(! x. f(x) & (! y. g(y) & h x y --> j x y) \ |
1465 | 365 |
\ --> (! y. g(y) & h x y --> k(y))) & \ |
366 |
\ ~ (? y. l(y) & k(y)) & \ |
|
367 |
\ (? x. f(x) & (! y. h x y --> l(y)) \ |
|
368 |
\ & (! y. g(y) & h x y --> j x y)) \ |
|
969 | 369 |
\ --> (? x. f(x) & ~ (? y. g(y) & h x y))"; |
2891 | 370 |
by (Blast_tac 1); |
969 | 371 |
result(); |
372 |
||
373 |
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374 |
writeln"Problems (mainly) involving equality or functions"; |
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375 |
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376 |
writeln"Problem 48"; |
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5150 | 377 |
Goal "(a=b | c=d) & (a=c | b=d) --> a=d | b=c"; |
2891 | 378 |
by (Blast_tac 1); |
969 | 379 |
result(); |
380 |
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381 |
writeln"Problem 49 NOT PROVED AUTOMATICALLY"; |
|
382 |
(*Hard because it involves substitution for Vars; |
|
383 |
the type constraint ensures that x,y,z have the same type as a,b,u. *) |
|
5150 | 384 |
Goal "(? x y::'a. ! z. z=x | z=y) & P(a) & P(b) & (~a=b) \ |
3842 | 385 |
\ --> (! u::'a. P(u))"; |
4153 | 386 |
by (Classical.Safe_tac); |
969 | 387 |
by (res_inst_tac [("x","a")] allE 1); |
388 |
by (assume_tac 1); |
|
389 |
by (res_inst_tac [("x","b")] allE 1); |
|
390 |
by (assume_tac 1); |
|
4353
d565d2197a5f
updated for latest Blast_tac, which treats equality differently
paulson
parents:
4153
diff
changeset
|
391 |
by (Fast_tac 1); (*Blast_tac's treatment of equality can't do it*) |
969 | 392 |
result(); |
393 |
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394 |
writeln"Problem 50"; |
|
395 |
(*What has this to do with equality?*) |
|
5150 | 396 |
Goal "(! x. P a x | (! y. P x y)) --> (? x. ! y. P x y)"; |
2891 | 397 |
by (Blast_tac 1); |
969 | 398 |
result(); |
399 |
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400 |
writeln"Problem 51"; |
|
5278 | 401 |
Goal "(? z w. ! x y. P x y = (x=z & y=w)) --> \ |
969 | 402 |
\ (? z. ! x. ? w. (! y. P x y = (y=w)) = (x=z))"; |
2891 | 403 |
by (Blast_tac 1); |
969 | 404 |
result(); |
405 |
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406 |
writeln"Problem 52"; |
|
407 |
(*Almost the same as 51. *) |
|
5278 | 408 |
Goal "(? z w. ! x y. P x y = (x=z & y=w)) --> \ |
969 | 409 |
\ (? w. ! y. ? z. (! x. P x y = (x=z)) = (y=w))"; |
2891 | 410 |
by (Blast_tac 1); |
969 | 411 |
result(); |
412 |
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413 |
writeln"Problem 55"; |
|
414 |
||
415 |
(*Non-equational version, from Manthey and Bry, CADE-9 (Springer, 1988). |
|
416 |
fast_tac DISCOVERS who killed Agatha. *) |
|
5150 | 417 |
Goal "lives(agatha) & lives(butler) & lives(charles) & \ |
969 | 418 |
\ (killed agatha agatha | killed butler agatha | killed charles agatha) & \ |
419 |
\ (!x y. killed x y --> hates x y & ~richer x y) & \ |
|
420 |
\ (!x. hates agatha x --> ~hates charles x) & \ |
|
421 |
\ (hates agatha agatha & hates agatha charles) & \ |
|
422 |
\ (!x. lives(x) & ~richer x agatha --> hates butler x) & \ |
|
423 |
\ (!x. hates agatha x --> hates butler x) & \ |
|
424 |
\ (!x. ~hates x agatha | ~hates x butler | ~hates x charles) --> \ |
|
425 |
\ killed ?who agatha"; |
|
2922 | 426 |
by (Fast_tac 1); |
969 | 427 |
result(); |
428 |
||
429 |
writeln"Problem 56"; |
|
5278 | 430 |
Goal "(! x. (? y. P(y) & x=f(y)) --> P(x)) = (! x. P(x) --> P(f(x)))"; |
2891 | 431 |
by (Blast_tac 1); |
969 | 432 |
result(); |
433 |
||
434 |
writeln"Problem 57"; |
|
5278 | 435 |
Goal "P (f a b) (f b c) & P (f b c) (f a c) & \ |
969 | 436 |
\ (! x y z. P x y & P y z --> P x z) --> P (f a b) (f a c)"; |
2891 | 437 |
by (Blast_tac 1); |
969 | 438 |
result(); |
439 |
||
440 |
writeln"Problem 58 NOT PROVED AUTOMATICALLY"; |
|
5150 | 441 |
Goal "(! x y. f(x)=g(y)) --> (! x y. f(f(x))=f(g(y)))"; |
969 | 442 |
val f_cong = read_instantiate [("f","f")] arg_cong; |
4089 | 443 |
by (fast_tac (claset() addIs [f_cong]) 1); |
969 | 444 |
result(); |
445 |
||
446 |
writeln"Problem 59"; |
|
5150 | 447 |
Goal "(! x. P(x) = (~P(f(x)))) --> (? x. P(x) & ~P(f(x)))"; |
2891 | 448 |
by (Blast_tac 1); |
969 | 449 |
result(); |
450 |
||
451 |
writeln"Problem 60"; |
|
5278 | 452 |
Goal "! x. P x (f x) = (? y. (! z. P z y --> P z (f x)) & P x y)"; |
2891 | 453 |
by (Blast_tac 1); |
969 | 454 |
result(); |
455 |
||
2715 | 456 |
writeln"Problem 62 as corrected in JAR 18 (1997), page 135"; |
5150 | 457 |
Goal "(ALL x. p a & (p x --> p(f x)) --> p(f(f x))) = \ |
458 |
\ (ALL x. (~ p a | p x | p(f(f x))) & \ |
|
459 |
\ (~ p a | ~ p(f x) | p(f(f x))))"; |
|
2891 | 460 |
by (Blast_tac 1); |
1404 | 461 |
result(); |
462 |
||
4463 | 463 |
(*From Davis, Obvious Logical Inferences, IJCAI-81, 530-531 |
464 |
Fast_tac indeed copes!*) |
|
465 |
goal Prod.thy "(ALL x. F(x) & ~G(x) --> (EX y. H(x,y) & J(y))) & \ |
|
466 |
\ (EX x. K(x) & F(x) & (ALL y. H(x,y) --> K(y))) & \ |
|
467 |
\ (ALL x. K(x) --> ~G(x)) --> (EX x. K(x) & J(x))"; |
|
468 |
by (Fast_tac 1); |
|
469 |
result(); |
|
470 |
||
1712 | 471 |
(*From Rudnicki, Obvious Inferences, JAR 3 (1987), 383-393. |
472 |
It does seem obvious!*) |
|
473 |
goal Prod.thy |
|
474 |
"(ALL x. F(x) & ~G(x) --> (EX y. H(x,y) & J(y))) & \ |
|
475 |
\ (EX x. K(x) & F(x) & (ALL y. H(x,y) --> K(y))) & \ |
|
476 |
\ (ALL x. K(x) --> ~G(x)) --> (EX x. K(x) --> ~G(x))"; |
|
4463 | 477 |
by (Fast_tac 1); |
1712 | 478 |
result(); |
479 |
||
6799
95abcc002a21
new classical example from Lewis Carroll via S G Pulman
paulson
parents:
5278
diff
changeset
|
480 |
(*Attributed to Lewis Carroll by S. G. Pulman. The first or last assumption |
95abcc002a21
new classical example from Lewis Carroll via S G Pulman
paulson
parents:
5278
diff
changeset
|
481 |
can be deleted.*) |
95abcc002a21
new classical example from Lewis Carroll via S G Pulman
paulson
parents:
5278
diff
changeset
|
482 |
Goal "(ALL x. honest(x) & industrious(x) --> healthy(x)) & \ |
95abcc002a21
new classical example from Lewis Carroll via S G Pulman
paulson
parents:
5278
diff
changeset
|
483 |
\ ~ (EX x. grocer(x) & healthy(x)) & \ |
95abcc002a21
new classical example from Lewis Carroll via S G Pulman
paulson
parents:
5278
diff
changeset
|
484 |
\ (ALL x. industrious(x) & grocer(x) --> honest(x)) & \ |
95abcc002a21
new classical example from Lewis Carroll via S G Pulman
paulson
parents:
5278
diff
changeset
|
485 |
\ (ALL x. cyclist(x) --> industrious(x)) & \ |
95abcc002a21
new classical example from Lewis Carroll via S G Pulman
paulson
parents:
5278
diff
changeset
|
486 |
\ (ALL x. ~healthy(x) & cyclist(x) --> ~honest(x)) \ |
95abcc002a21
new classical example from Lewis Carroll via S G Pulman
paulson
parents:
5278
diff
changeset
|
487 |
\ --> (ALL x. grocer(x) --> ~cyclist(x))"; |
95abcc002a21
new classical example from Lewis Carroll via S G Pulman
paulson
parents:
5278
diff
changeset
|
488 |
by (Blast_tac 1); |
95abcc002a21
new classical example from Lewis Carroll via S G Pulman
paulson
parents:
5278
diff
changeset
|
489 |
result(); |
95abcc002a21
new classical example from Lewis Carroll via S G Pulman
paulson
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5278
diff
changeset
|
490 |
|
1712 | 491 |
goal Prod.thy |
492 |
"(ALL x y. R(x,y) | R(y,x)) & \ |
|
493 |
\ (ALL x y. S(x,y) & S(y,x) --> x=y) & \ |
|
494 |
\ (ALL x y. R(x,y) --> S(x,y)) --> (ALL x y. S(x,y) --> R(x,y))"; |
|
2891 | 495 |
by (Blast_tac 1); |
1712 | 496 |
result(); |
497 |
||
498 |
||
499 |
||
969 | 500 |
writeln"Reached end of file."; |