fact: {} -> PROPAGATE
x = 1
fact: {x: 1}
y = 2
fact: {x: 1, y: 2}
~z = x + y~~
{x: 1, y : 2, z: 3} -> REWRITE + PROPAGATE
z = 3
-- :( rewrite, propagate. --
fact: {} -> PROPAGATE
x = 1
fact: {x: 1}
y = 2
fact: {x: 1, y: 2}
~z = x + y~~
{x: 1, y : 2} -> REWRITE
z = 3 <- NEW statement from the REWRITE;
fact: {x: 1, y: 2, z: 3}
x = 2 * 10 ; (x = 20; x is EVEN)
y = 2 * z; (y = UNK; y is EVEN)
-> if (y %2 == 0) { T } else { E }
T -> analysis