#include <string.h>
#include <other.h>
/*
	Perform one transaction interactivly.

	The function returns only when transaction is secure.
*/
int xsys_transact (void)
{
	....
}

/*
	Undo the last transaction.

	This function must be called only in this and this and this
	situation.

	Return -1 if transaction can't be undone.
*/
int xsys_undo (void)
{
}