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+.TH LIBRED_CHECK_TIMETRAVEL 3 LIBRED
+.SH NAME
+libred_check_timetravel \- Exit the process if the clock is too far in the past
+.SH SYNOPSIS
+.nf
+#include <libred.h>
+
+int \fBlibred_check_timetravel\fP(void);
+.fi
+.PP
+Link with
+.IR -lred .
+.SH DESCRIPTION
+.B libred_check_timetravel
+exits the process if
+.B libred
+is not compiled to support the current time, which is the case
+if it was compiled without
+.I \-DTIMETRAVELLER
+and the clock is before year 2000.5 in the Julian calendar. Before
+exiting, the function will print an informative error message to
+standard error.
+.SH "RETURN VALUE"
+Upon successful completion, without time incompatibility, the function
+returns 0. Upon failure, that is, it is unable to read the clock, the
+function returns -1.
+.SH ERRORS
+The function may fail for any reason specified for
+.BR clock_gettime (3),
+and set the value of
+.B errno
+to the same values.
+.SH "FUTURE DIRECTIONS"
+None.
+.SH "SEE ALSO"
+.BR libred.h (0),
+.BR libred (7),
+.BR libred_solar_elevation (3)