% pocl1.epi

pair(x,y) := (x,y).

Set.dom() := self.collect(x::hd x).

Set.rng() := self.collect(x::hd(tl x)).

Set.ds(aSet):= self.select(x::aSet.member(hd (tl x))).

Set.at(k):= self.exists(x::hd(x)=k) then hd(tl(self.locate(x::hd(x)=k)))
                                    else nil.
									
									
									
people := set().add(1).add(2).add(3).
offices:= set().add(11).add(12).

pm := set().add(pair(1,45)).add(pair(2,45)).
pm1 := set().add(pair(1,45)).
pm2 := set().add(pair(2,45)).

po := set().add(pair(1,11)).add(pair(2,12)).

s:= channel().

centre(pm,po):=
  in(s, (b,r)::out(r,pm.at(b), centre(pm.ds(set().add(b)), po))).
  
office(pm,d,r):= 
  	people.alt(b::
		pm.dom().member(b) then out(d,b,office(pm.ds(set().add(b)), d,r))
		                   else out(s, (b,r), in(r,x::office(pm,d,r)))).
						   
sink(c) := in(c, x::sink(c)).

p:= par(centre(pm,po),
    par(par(office(pm1,91,11), sink(91)),
	    par(office(pm2,92,12), sink(92)))).