reserve V, C for set;
reserve A, B, D for Element of Fin PFuncs (V, C);
reserve s for Element of PFuncs (V,C);

theorem Th23:
  B c= B ^ B
proof
  now
    let a be set;
    assume
A1: a in B;
    B c= PFuncs (V, C) by FINSUB_1:def 5;
    then reconsider a9 = a as Element of PFuncs (V,C) by A1;
    a = a \/ a & a9 tolerates a9;
    hence a in B ^ B by A1;
  end;
  hence thesis;
end;
