I got an undeclared identifier error for the following Pine Script script, but don't know why.

//@version=4

study("NAME")

plot(close)

var A = array.new_int(0)

var B = array.new_int(0)

if (true)

    if (true)

        y = array.get(B, 0)
        if(true)

            box.delete(box.new(1,1,1,1))
            array.push(A, 1)
        else

            array.push(A, 1)

    y = array.get(A, 0)

The error:

"line 12: Undeclared identifier 'B';
line 17: Variable 'y' is not found in scope 'global_#0_#0', cannot register side effect"