Sémantique Axiomatique ou Logique de Hoare - Ensiie

Come back to the conditional example
To end the proof we can use twice the logical rule.
Let us detail the proof !
From x > 2 ⇒ 1 > 0 (valid formula why ?) and
from {1 > 0}y := 1{y > 0}
we can deduce (with the logical rule on preconditions)
{x > 2}y := 1{y > 0} (1)
and also from false ⇒ (−1 > 0) (valid ! why ?) and from
{−1 > 0}y := −1{y > 0}
we can deduce (with the logical rule on preconditions)
{false}y := −1{y > 0} (2)
Altogether we obtain an inference tree (or derivation tree) that sums up
the demonstration and the way we have reasoned.
(ENSIIE) Hoare 24 / 52