reserve r,t for Real;
reserve i for Integer;
reserve k,n for Nat;
reserve p for Polynomial of F_Real;
reserve e for Element of F_Real;
reserve L for non empty ZeroStr;
reserve z,z0,z1,z2 for Element of L;

theorem Th7:
  sin(7*PI/6) = -1/2
  proof
    7*PI/6 = PI+PI/6;
    hence thesis by EUCLID10:17,SIN_COS:79;
  end;
