When building the physical IFG, we step backwards in each block, and remove things that are defined from the LIVE_OUT, (and lower the current pressure) and add input to the LIVE_OUT (and raising the current pressure). Each time we lower or raise the current pressure, we check if it's bigger than the current maximum pressure, known as final_pressure. However the final_pressure can never increase when removing definitions (i.e. lower the current pressure) so the check for a new final_pressure in Pressure::lower is useless.