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procedure P0()
{
var x: int where 0 <= x;
var y: int where x <= y;
assert 0 <= x;
assert x <= y;
assert y < 5; // error
}
procedure P1()
{
var x: int where 0 <= x;
var y: int where x <= y;
x := 5;
havoc y;
assert 5 <= y;
havoc x;
assert 0 <= x;
assert x <= y; // error
}
procedure P2()
{
var x: int where 0 <= x;
var y: int where x <= y;
havoc y; // y first
havoc x;
assert x <= y; // error
}
procedure P3()
{
var x: int where 0 <= x;
var y: int where x <= y;
x := 5;
havoc x; // this time, x first
havoc y;
assert x <= y; // yeah!
assert 5 <= y; // error
}
procedure P4()
{
var x: int where 0 <= x;
var y: int where x <= y;
havoc x, y; // both at the same time
assert 0 <= x && x <= y;
havoc y, x; // or in the other order
assert 0 <= x && x <= y;
assert x == 7; // error
}
procedure R0() returns (wProc: int where wProc == xProc,
xProc: int where 0 <= xProc,
yProc: int where xProc <= yProc);
implementation R0() returns (w: int, x: int, y: int)
{
while (*) {
assert w == x;
assert 0 <= x;
assert x <= y;
}
while (*) {
assert w == x;
assert 0 <= x;
assert x <= y;
// the following makes w, x, y loop targets
w := w + 1;
havoc x;
y := w;
}
assert w == x;
assert 0 <= x;
assert x <= y;
}
procedure R1()
{
var a: int;
var b: int;
var c: int;
call a, b, c := R0();
assert a == b;
assert 0 <= b;
assert b <= c;
}
procedure R2()
{
var w: int where w == x;
var x: int where 0 <= x;
var y: int where x <= y;
x := 5;
y := 10;
while (*) {
w := w + 1;
assert w == 6;
y := y + 2;
assert 7 <= y;
}
assert x == 5 && 0 <= y - w;
assert y == 10; // error
}
procedure R3()
{
var w: int where w == x;
var x: int where 0 <= x;
var y: int where x <= y;
// change w and x
y := 10;
while (*) {
w := w; x := x;
}
assert w == x;
assert 0 <= x;
assert y == 10;
assert w <= 10; // error
}
procedure R4()
{
var w: int where w == x;
var x: int where 0 <= x;
var y: int where x <= y;
// change x and y
w := 12;
while (*) {
x := x; y := y;
}
assert 0 <= x;
assert x <= y;
assert w == 12;
assert 8 <= y; // error
}
procedure R5(K: int)
{
var w: int where w == x;
var x: int where 0 <= x;
var y: int where x <= y;
// change w and y
x := K;
while (*) {
w := w; y := y;
}
assert w == K;
assert K <= y;
assert x == K;
assert 0 <= x; // error
}
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