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 Source: David Merchat (node swimingpool)

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node First( X : int ) returns ( First : int );

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let

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First = X > pre First;

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tel

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node Sofar( X : bool ) returns ( Sofar : bool );

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let

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Sofar = X > X and pre Sofar;

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tel

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node excludes6( X1, X2, X3, X4, X5, X6 : bool ) returns ( excludes : bool );

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let

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excludes = not X1 and not X2 and not X3 and not X4 and not X5 and not X6 or

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X1 and not X2 and not X3 and not X4 and not X5 and not X6 or

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not X1 and X2 and not X3 and not X4 and not X5 and not X6 or

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not X1 and not X2 and X3 and not X4 and not X5 and not X6 or

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not X1 and not X2 and not X3 and X4 and not X5 and not X6 or

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not X1 and not X2 and not X3 and not X4 and X5 and not X6 or

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not X1 and not X2 and not X3 and not X4 and not X5 and X6;

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tel

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node swimingpool(e1, e2, e3, e4, e5, e6 : bool;init_p1, init_p2 : int)returns

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(x1, x2, x3, x4, x5, x6, x7, p1, p2 : int);

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var

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g1, g2, g3, g4, g5, g6 : bool;

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let

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g1 = false > pre x6>=1;

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g2 = false > pre x1>=1 and pre x7>=1;

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g3 = false > pre x2>=1;

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g4 = false > pre x3>=1 and pre x6>=1;

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g5 = false > pre x4>=1;

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g6 = false > pre x5>=1;

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x1 = 0 >

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if(e1) then if(g1) then pre x1+1 else pre x1 else

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if(e2) then if(g2) then pre x11 else pre x1 else

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pre x1;

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x2 = 0 >

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if(e2) then if(g2) then pre x2+1 else pre x2 else

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if(e3) then if(g3) then pre x21 else pre x2 else

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pre x2;

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x3 = 0 >

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if(e3) then if(g3) then pre x3+1 else pre x3 else

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if(e4) then if(g4) then pre x31 else pre x3 else

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pre x3;

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x4 = 0 >

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if(e4) then if(g4) then pre x4+1 else pre x4 else

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if(e5) then if(g4) then pre x41 else pre x4 else

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pre x4;

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x5 = 0 >

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if(e5) then if(g5) then pre x5+1 else pre x5 else

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if(e6) then if(g6) then pre x51 else pre x5 else

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pre x5;

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x6 = p1 >

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if(e1) then if(g1) then pre x61 else pre x6 else

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if(e3) then if(g3) then pre x6+1 else pre x6 else

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if(e4) then if(g4) then pre x61 else pre x6 else

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if(e6) then if(g6) then pre x6+1 else pre x6 else

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pre x6;

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x7 = p2 >

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if(e2) then if(g2) then pre x71 else pre x7 else

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if(e5) then if(g5) then pre x7+1 else pre x7 else

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pre x7;

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p1 = init_p1 >

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pre p1;

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p2 = init_p2 >

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pre p2;

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tel

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node top(e1, e2, e3, e4, e5, e6 : bool;init_p1, init_p2 : int)

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returns ( OK : bool );

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@ contract guarantees OK;

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var x1, x2, x3, x4, x5, x6, x7, p1, p2 : int;

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env : bool;

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let

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(x1, x2, x3, x4, x5, x6, x7, p1, p2) =

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swimingpool(e1, e2, e3, e4, e5, e6, init_p1, init_p2);

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env = Sofar( excludes6( e1, e2, e3, e4, e5, e6 ) ) and

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0 <= First(init_p1) and 0 <= First(init_p2) and First(init_p1) < 1000 and First(init_p2) < 1000;

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OK = env => x2 < 1;

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%PROPERTY OK=true;

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%MAIN;

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tel
