Incorrect Answer.
The program P:
x = y;
if (x < z) { x = z; }
satisfies the Hoare triple
x = y 
P x = y
with respect to the partial correctness relation 
par, if
at any state satisfying "x = y", if the program
P terminates, then the resulting store satisfies "x = y".
While the first assignment statement "x = y;" maintains the property
that the values of x and y are equal, the if-statement may change that,
provided that the value of x is less than the value of z.
For then x will obtain the value of z which is different from the value of
y (since x and y have the same value in the current store in which x is
less than z). For example, consider the initial store in which the
values of x, y, and z are 2, 3, and 4, respectively.
If P begins executing in that store, it terminates
such that the values of x and y will be 4 and 3, respectively.
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