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
i:Id.
if isnull(a(i;t-1))
first(<i,t-1>) else false
fi
if isnull(a(i;t-1)) pred(<i,t-1>) else <i,t-1> fi <loc <i,t>
& (e':E.
& ((if isnull(a(i;t-1)) pred(<i,t-1>) else <i,t-1> fi <loc e'
& ((& e' <loc <i,t>))
