sed 's/   */|/g;/^ *$/d' input.txt | awk -F"|" ' { print $1 } ' | sort | uniq -ud

sed 's/   */|/g;/^ *$/d' input.txt | awk -F"|" ' { print $1 } ' | sort | uniq -ud | grep [A-Z][A-Z][A-Z]*

sed 's/   */|/g;/^ *$/d' input.txt | awk -F"|" ' { print $1 } ' | sort | uniq -ud | grep -v [A-Z][A-Z][A-Z]*

EVENT
INTERNET CONNECTION
Date                       11/01/2009
Initial hour               07:30
Number of users            27
Average of use             32 min
Final hour                 19:00
EVENT
LOCAL CALL
Date                       11/01/2009
Initial hour               07:42
Number of users            15
Average of use             7 min
Final hour                 16:11
EVENT
INTERNATIONAL CALL
Date                       11/01/2009
Initial hour               09:14
Number of users            21
Average of use             5 min
Final hour                 16:17
EVENT
PRINTER USE
Date                       12/01/2009
Initial hour               07:30
Number of users            23
Average of pages printed   17
Final hour                 19:00

Average of pages printed
Average of use
Date
EVENT
Final hour
INTERNATIONAL CALL
INTERNET CONNECTION
Initial hour
LOCAL CALL
Number of users
PRINTER USE

EVENT
INTERNATIONAL CALL
INTERNET CONNECTION
LOCAL CALL
PRINTER USE

Average of pages printed
Average of use
Date
Final hour
Initial hour
Number of users