
theorem Th10:
  for R being DB-Rel, A, B being Subset of the Attributes of R
  holds [A, B] in Dependency-str R iff A >|> B, R
proof
  let D be DB-Rel, A, B be Subset of the Attributes of D;
  set S = Dependency-str D;
  hereby
    assume [A, B] in S;
    then consider a, b being Subset of the Attributes of D such that
A1: [A, B] = [a, b] and
A2: a >|> b, D;
    A = a by A1,XTUPLE_0:1;
    hence A >|> B, D by A1,A2,XTUPLE_0:1;
  end;
  thus thesis;
end;
