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1 -- C97201X.ADA
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2
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3 -- Grant of Unlimited Rights
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4 --
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5 -- Under contracts F33600-87-D-0337, F33600-84-D-0280, MDA903-79-C-0687,
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6 -- F08630-91-C-0015, and DCA100-97-D-0025, the U.S. Government obtained
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7 -- unlimited rights in the software and documentation contained herein.
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8 -- Unlimited rights are defined in DFAR 252.227-7013(a)(19). By making
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9 -- this public release, the Government intends to confer upon all
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10 -- recipients unlimited rights equal to those held by the Government.
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11 -- These rights include rights to use, duplicate, release or disclose the
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12 -- released technical data and computer software in whole or in part, in
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13 -- any manner and for any purpose whatsoever, and to have or permit others
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14 -- to do so.
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15 --
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16 -- DISCLAIMER
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17 --
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18 -- ALL MATERIALS OR INFORMATION HEREIN RELEASED, MADE AVAILABLE OR
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19 -- DISCLOSED ARE AS IS. THE GOVERNMENT MAKES NO EXPRESS OR IMPLIED
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20 -- WARRANTY AS TO ANY MATTER WHATSOEVER, INCLUDING THE CONDITIONS OF THE
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21 -- SOFTWARE, DOCUMENTATION OR OTHER INFORMATION RELEASED, MADE AVAILABLE
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22 -- OR DISCLOSED, OR THE OWNERSHIP, MERCHANTABILITY, OR FITNESS FOR A
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23 -- PARTICULAR PURPOSE OF SAID MATERIAL.
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24 --*
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25 -- CHECK THAT NO RENDEZVOUS CAN EVER OCCUR IF BOTH PARTNERS REFUSE TO
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26 -- WAIT (THAT IS, IF THE ENTRY CALL IS ISSUED BY A
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27 -- "CONDITIONAL_ENTRY_CALL" AND THUS FOLLOWS A NO-WAIT POLICY
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28 -- (DEMANDING UNCONDITIONALLY THAT "YOU DO IT N O W , OR ELSE"),
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29 -- WHILE THE CALLEE IS ALSO COMMITTED TO A NO-WAIT POLICY,
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30 -- BY VIRTUE OF A SELECTIVE_WAIT STATEMENT OF THE THIRD KIND
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31 -- (WITH AN "ELSE" PART) IN WHICH THE CORRESPONDING ACCEPT_STATEMENT
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32 -- IS EMBEDDED).
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33 -- ("CLOSE ENCOUNTERS OF THE THIRD KIND" -- ARE THEY POSSIBLE?)
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34
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35
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36 -- THE SEMANTICS OF THIS ENTRY CALL REQUIRES THAT THE CALLING TASK
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37 -- N O T ENTER ITSELF ON ANY QUEUE BUT RATHER ATTEMPT AN IMMEDIATE
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38 -- RENDEZVOUS WHICH IS TO TAKE PLACE IF AND ONLY IF THE CALLED TASK
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39 -- HAS REACHED A POINT WHERE IT IS READY TO ACCEPT THE CALL (I.E.
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40 -- IT IS EITHER WAITING AT AN ACCEPT STATEMENT FOR THE CORRESPONDING
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41 -- ENTRY OR IT IS WAITING AT A SELECTIVE_WAIT STATEMENT WITH AN OPEN
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42 -- ALTERNATIVE STARTING WITH SUCH AN ACCEPT STATEMENT). IT ALSO
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43 -- REQUIRES THAT THE ENTRY CALL BE CANCELLED IF THE CALLED TASK
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44 -- IS NOT AT SUCH A POINT. ON THE OTHER HAND, THE SEMANTICS OF THE
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45 -- SELECTIVE_WAIT STATEMENT WITH AN 'ELSE' PART SPECIFIES THAT
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46 -- THE 'ELSE' PART MUST BE SELECTED IF NO 'ACCEPT' ALTERNATIVE
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47 -- CAN BE IMMEDIATELY SELECTED, AND THAT SUCH AN ALTERNATIVE
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48 -- IS DEEMED TO BE IMMEDIATELY SELECTABLE ("SELECTION OF ONE SUCH
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49 -- ALTERNATIVE OCCURS IMMEDIATELY"), AND A CORRESPONDING RENDEZVOUS
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50 -- POSSIBLE, IF AND ONLY IF THERE IS A CORRESPONDING ENTRY CALL
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51 -- W A I T I N G TO BE ACCCEPTED. A "CONDITIONAL ENTRY CALL"
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52 -- NEVER WAITS, AND IS NEVER ENTERED IN WAIT QUEUES; IT TAKES
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53 -- THE 'ELSE' PART INSTEAD.
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54
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55
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56 -- NOTE: IF THIS TEST PROGRAM HANGS UP, THE COMPILER WILL BE DEEMED
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57 -- TO HAVE FAILED.
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58
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59
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60 -- RM 3/19/82
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61
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62
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63 WITH REPORT; USE REPORT;
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64 PROCEDURE C97201X IS
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65
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66 RENDEZVOUS_OCCURRED : BOOLEAN := FALSE ;
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67
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68 CALLER_TAKES_WRONG_BRANCH : BOOLEAN := TRUE ;
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69 SERVER_TAKES_WRONG_BRANCH : BOOLEAN := TRUE ;
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70 QUEUE_NOT_EMPTY : BOOLEAN := FALSE ;
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71
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72 BEGIN
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73
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74
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75 TEST ("C97201X", "CHECK THAT NO RENDEZVOUS CAN EVER OCCUR IF" &
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76 " BOTH PARTNERS REFUSE TO WAIT" );
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77
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78
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79 DECLARE
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80
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81
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82 TASK T IS
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83 ENTRY SYNCHRONIZE ;
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84 ENTRY DO_IT_NOW_ORELSE( DID_YOU_DO_IT : IN OUT BOOLEAN);
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85 ENTRY KEEP_ALIVE ;
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86 END T ;
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87
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88
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89 TASK BODY T IS
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90 BEGIN
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91
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92
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93 ACCEPT SYNCHRONIZE ;
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94
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95
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96 IF DO_IT_NOW_ORELSE'COUNT /= 0 THEN
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97 QUEUE_NOT_EMPTY := TRUE ;
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98 END IF;
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99
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100
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101 SELECT
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102 ACCEPT DO_IT_NOW_ORELSE
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103 ( DID_YOU_DO_IT : IN OUT BOOLEAN )
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104 DO
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105 DID_YOU_DO_IT := TRUE ;
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106 END ;
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107 ELSE -- (I.E. TASK ADOPTS NO-WAIT POLICY)
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108 -- 'ELSE' BRANCH MUST THEREFORE BE CHOSEN
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109 SERVER_TAKES_WRONG_BRANCH := FALSE ;
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110 END SELECT;
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111
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112
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113 IF DO_IT_NOW_ORELSE'COUNT /= 0 THEN
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114 QUEUE_NOT_EMPTY := TRUE ;
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115 END IF;
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116
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117
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118 ACCEPT KEEP_ALIVE ; -- TO PREVENT THIS SERVER TASK FROM
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119 -- TERMINATING IF IT GETS TO
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120 -- THE NO-WAIT MEETING-PLACE
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121 -- AHEAD OF THE CALLER (WHICH
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122 -- WOULD LEAD TO A SUBSEQUENT
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123 -- TASKING_ERROR AT THE TIME OF
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124 -- THE NO-WAIT CALL).
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125
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126
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127 END T ;
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128
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129
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130 BEGIN
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131
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132
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133 T.SYNCHRONIZE ; -- TO MINIMIZE THE N E E D TO WAIT
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134
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135
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136 SELECT
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137 T.DO_IT_NOW_ORELSE ( RENDEZVOUS_OCCURRED );
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138 ELSE -- (I.E. CALLER TOO ADOPTS A NO-WAIT POLICY)
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139 -- MUST THEREFORE CHOOSE THIS BRANCH
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140 CALLER_TAKES_WRONG_BRANCH := FALSE ;
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141 END SELECT;
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142
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143
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144 T.KEEP_ALIVE ; -- THIS ALSO UPDATES THE NONLOCALS
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145
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146
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147 END; -- END OF BLOCK CONTAINING THE NO-WAIT ENTRY CALL
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148
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149
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150 IF RENDEZVOUS_OCCURRED
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151 THEN
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152 FAILED( "RENDEZVOUS OCCURRED" );
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153 END IF;
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154
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155 IF CALLER_TAKES_WRONG_BRANCH OR
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156 SERVER_TAKES_WRONG_BRANCH
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157 THEN
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158 FAILED( "WRONG BRANCH TAKEN" );
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159 END IF;
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160
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161 IF QUEUE_NOT_EMPTY
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162 THEN
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163 FAILED( "ENTRY QUEUE NOT EMPTY" );
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164 END IF;
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165
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166
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167 RESULT;
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168
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169
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170 END C97201X ;
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