input:n(0.05);a1:=ma(c,5);a2:=ma(c,10);a3:=ma(c,20);abs(a1/a2-1)<n and abs(a1/a3-1)<nand abs(a3/a2-1)<n and cross(c,a1)and cross(c,a1) and cross(c,a1)and c>o;