begin   
comment using c-functions asin and acos;	
	
	real procedure arcsin(real VALUE a); algol "asin"; 
	real procedure arccos(real VALUE a); algol "acos"; 
   
	real r;
	r := arcsin(1); comment pi/2;
	write(r);
	r := arccos(0.5); comment pi/3;
	write(r);
end