theorem
  for V being add-associative right_zeroed right_complementable Abelian
    scalar-distributive scalar-unital scalar-associative vector-distributive
    non empty RLSStruct
  for f1,f2 being PartFunc of C,V holds
  f1 - (-f2) = f1 + f2
proof
  let V be add-associative right_zeroed right_complementable Abelian
  scalar-distributive scalar-unital scalar-associative vector-distributive
  non empty RLSStruct;
  let f1,f2 be PartFunc of C,V;
  thus f1 - (-f2) = f1 + (-(-f2)) by Th25
    .= f1 + f2 by Th24;
end;
