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var b: bool;
procedure p0();
requires b;
modifies b;
ensures (lambda x: bool :: old(b))[true];
ensures !(lambda x: bool :: b)[true];
implementation p0()
{
b := !b;
assert (lambda x: bool :: old(b))[true];
assert !(lambda x: bool :: b)[true];
}
procedure p1();
requires !b;
modifies b;
ensures (lambda x: bool :: old(b))[true]; // error
implementation p1()
{
b := !b;
assert !(lambda x: bool :: old(b))[true];
}
procedure p2();
requires b;
modifies b;
ensures (lambda x: bool :: old(b) != b)[true];
implementation p2()
{
b := !b;
assert (lambda x: bool :: old(b) != b)[true];
}
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