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Signed-off-by: Mattias Andrée <m@maandree.se>

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+NAME
+	luhncheck - Check number with Luhn's algorithm
+
+SYNOPSIS
+	luhncheck number ...
+
+DESCRIPTION
+	The luhncheck utility checks that a number, containing a
+	check digit, is valid according to Luhn's algorithm.
+
+OPTIONS
+	The luhncheck utility conforms to the Base Definitions volume
+	of POSIX.1-2017, Section 12.2, Utility Syntax Guidelines.
+
+	No options are supported.
+
+OPERANDS
+	The following operand is supported:
+
+	number
+		Number to check.
+
+STDOUT
+	The luhncheck utility will print one line per number, in the
+	order they are provided in the command line, to the standard
+	output. Each line will be use the format
+
+		"%s is %s\n", number, <"OK" if valid, "invalid" otherwise>.
+
+EXIT STATUS
+	The following exit values are returned:
+
+	0	All numbers are valid.
+
+	1	At least one number is invalid.
+
+	2	An error occured.
+
+SEE ALSO
+	gluhncheck(1)