Serial Monitor statements

ok, here's the code. please dont laugh...

boolean above = true;
boolean below = false;

void setup() {
Serial.begin(9600);

}

void loop() {
int sensorValue = analogRead(A0);

if (sensorValue < 500)
{
if (above = true)
{
Serial.println("oh, i'm down!");
above = false;
below = true;
// here i try to "lock the door", once the line is printed. But it still doesn't work....
}
}
else
{
Serial.println("Oh, i'm Up!");
above = true;
below = false;

}
}