theorem
  for T being quasi-type of C for f1,f2 being valuation of C
  holds (T at f1) at f2 = T at (f1 at f2)
proof
  let T be quasi-type of C;
  let f1,f2 be valuation of C;
  thus (T at f1) at f2
  = (((adjs T) at f1) at f2)ast((the_base_of (T at f1))at f2)
    .= ((adjs T) at (f1 at f2))ast((the_base_of (T at f1))at f2) by Th150
    .= ((adjs T) at (f1 at f2))ast(((the_base_of T) at f1)at f2)
    .= T at (f1 at f2) by Th149;
end;
