A concurrent signal assignment statement that includes the option guarded, which specifies that the signal assignment statement is executed when a signal GUARD changes from FALSE to TRUE, or when that signal has been TRUE and an event occurs on one of the signals referenced in the corresponding GUARD expression. The signal GUARD may be one of the implicitly declared GUARD signals associated with block statements that have guard expressions, or it may be an explicitly declared signal of type Boolean that is visible at the point of the concurrent signal assignment statement.