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<?php $test = []; var_dump(is_set($test['key']));
based on MMbEZ
Finding entry points
Branch analysis from position: 0
1 jumps found. (Code = 62) Position 1 = -2
filename:       /in/KD24m
function name:  (null)
number of ops:  9
compiled vars:  !0 = $test
line     #* E I O op                           fetch          ext  return  operands
-------------------------------------------------------------------------------------
   3     0  E >   ASSIGN                                                   !0, <array>
   5     1        INIT_FCALL                                               'var_dump'
         2        INIT_FCALL_BY_NAME                                       'is_set'
         3        FETCH_DIM_FUNC_ARG                               $2      !0, 'key'
         4        SEND_VAR_EX                                              $2
         5        DO_FCALL                                      0  $3      
         6        SEND_VAR                                                 $3
         7        DO_ICALL                                                 
         8      > RETURN                                                   1

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