
theorem
  arcsin (1/2) = PI/6 & arcsin (sqrt 3 / 2) = PI/3
  proof
    PI/6 < PI/2 & PI/3 < PI/2 & -PI/2<= PI/6 & -PI/2<=PI/3
    by XREAL_1:76,COMPTRIG:5;
    hence thesis by Thm9,Thm11,SIN_COS6:69;
  end;
