This property of a href="module.php?name=Lexikon&file=search&eid=1&query=reduction">reduction system states that if an expression can be reduced by zero or more reduction steps to either expression M or expression N then there exists some other expression to which both M and N can be reduced. This implies that there is a unique href="module.php?name=Lexikon&file=search&eid=1&query=normal form">normal form for any expression since M and N cannot be different normal forms because the theorem says they can be reduced to some other expression and normal forms are irreducible by definition. It does not imply that a normal form is reachable, only that if reduction terminates it will reach a unique normal form. (1995-01-25)
