2. FairFifo
3.
e,e':E. loc(e) = loc(e') 
e <c e' 
e = e' e' <c e
4.
e:E. first(e) 
(e':E. loc(e') = loc(e) 
e' <c e)
5. t :
6. 0<t
7.
i:Id.
7.
first(<i,t-1>)
7.
7. pred(<i,t-1>) <loc <i,t-1>
7. & (
e':E. (pred(<i,t-1>) <loc e' & e' <loc <i,t-1>))
8.
t = 0
9. i : Id
10.
isnull(a(i;t-1))
false
<i,t-1> <loc <i,t> & (e':E. (<i,t-1> <loc e' & e' <loc <i,t>))
