reserve X for set;
reserve a,b,c,k,m,n for Nat;
reserve i,j for Integer;
reserve r for Real;
reserve p,p1,p2 for Prime;

theorem
  n satisfies_Sierpinski_problem_87a & n <= 27 implies n in {13,17,21,23,27}
  proof
    assume
A1: n satisfies_Sierpinski_problem_87a;
    assume n <= 27;
    then n = 0 or ... or n = 27;
    hence thesis by A1,Lm5,Lm6,
    Lm7,Lm8,Lm9,Lm10,Lm11,Lm12,Lm13,Lm14,Lm15,Lm16,
    Lm17,Lm18,Lm19,Lm20,Lm21,Lm22,Lm23,Lm24,Lm25,
    Lm26,Lm27,ENUMSET1:def 3;
  end;
