1               /
   2               / Check whether IFNZRO EXPR is true when EXPR refers to an undefined
   3               / symbol.  Treating it as such will cause TSS/8 assembly to fail.
   4               / A similar bug exists where 
   5               /
   6               *200
   7 000200  7000  START,  NOP
   8                       /IFZERO FOO1 <HLT>
   9 000201  7402          IFNZRO FOO1 <HLT>
  10               FOO1,   NOP     / Should not move between passes 1 and 2.
redefined          ^
     000202  7000  
  11 000203  7402          HLT
  12               $