theorem
  \2(T,I) value_at (C,u) = 2
  proof
A1: \1(T,I) value_at(C,u) = 1 by Th52;
    thus \2(T,I) value_at(C,u)
    = (\1(T,I) value_at(C,u))+(\1(T,I) value_at(C,u)) by Th54
    .= 2 by A1,AOFA_A00:55;
  end;
