procedure vdiff(var v1,v2,v3: vector);
var
  n: integer;
begin { vdiff }
  for n:=0 to vdim-1 do sdiff(v1[n],v2[n],v3[n]);
  ssum(v1[vdim],v2[vdim],v3[vdim]);
end { vdiff };