if a == null then printn(0) else printn(1)
if a is null then printn(0) else printn(1)
#if b == null then printn(1) else printn(0)
if a == null then printn(0) else printn(1)
if a is null then printn(0) else printn(1)
#if b == null then printn(1) else printn(0)