R-loc(R)
== case R of
== Rnone =>
== Rplus(left,right)=>rec1,rec2.
== Rinit(loc,T,x,v)=> loc == Rframe(loc,T,x,L)=> loc == Rsframe(lnk,tag,L)=> source(lnk)
== Reffect(loc,ds,knd,T,x,f)=> loc == Rsends(ds,knd,T,l,dt,g)=> source(l)
== Rpre(loc,ds,a,T,P)=> loc == Raframe(loc,k,L)=> loc == Rbframe(loc,k,L)=> loc == Rrframe(loc,x,L)=> loc