1 02/08/85  date_time_valid, dtv
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 3 Syntax as a command:  dtv time_string
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 6 Syntax as an active function:  [dtv time_string]
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 9 Function: returns "true" if the argument is a valid date-time string,
10 "false" otherwise.
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12 
13 Arguments:
14 time_string
15    is a string that is checked.  Since the concatenation of all the
16    arguments is checked, the argument need not be quoted if it contains
17    white space. (See time_strings.gi for a description of valid
18    time_string values.)