2. x : Id
3. i : Id
4. T : Type
5. c : T
6.
x,y:T. Dec(x = y)
7. vartype(i;x)
r T
8.
e:E. loc(e) = i 
(x when e) 
T
9.
e:E. loc(e) = i (x after e) T
10.
e:E. loc(e) = i first(e) (x when e) = c
11. e' : E
12. loc(e') = i
13.
(x after e') = c
14. e : E
15. first(e)
16. e
e'
17. (x when e) = c
(x after e') = (x when e) T
