function bind( x :tree; val :tree; e :Env ) :Env;
   var b :Env;
begin new(b);
      b^.id := x^.vid; b^.index := x^.index; b^.v := val;
      b^.next := e; bind := b
end;

function bound( x :tree; var val :tree; e :Env ) :boolean;
begin if e=nil then bound := false
      else if (e^.id=x^.vid) and (e^.index=x^.index) then
         begin val := e^.v; bound := true end
      else bound := bound( x, val, e^.next )
end;

{\fB Manipulate Environments. \fP}