begin
theorem Th1:
theorem Th2:
theorem Th3:
theorem Th4:
theorem
theorem Th6:
theorem Th7:
begin
:: deftheorem defines Catalan CATALAN1:def 1 :
theorem Th8:
theorem Th9:
theorem
theorem Th11:
theorem Th12:
theorem Th13:
theorem Th14:
theorem Th15:
theorem Th16:
theorem
theorem Th18:
theorem Th19:
theorem Th20:
theorem