Algorithm analysis

Conditional statement post condition

1:if (x < y) then
2: x <- y + z
3:else
4:x <- z
5:z <- z + 2
6:end if
pre(1) = (x < z) and (x > 0) and (y > 0) and (z > 0).

Find pre(2), pre(4)
post(2), post(4) and post(5)
for post which rule was used?(sub or forget)

plz i need help