f(x)=x^2-2
a=0
b=2
cold=0
while true
    c=(a+b)/2
    if cold==c
        break
    end
    global cold=c
    println("sqrt(2)=",c," p/m ",(b-a)/2)
    if f(c)>0
        global b=c
    else
        global a=c
    end
end