5.4 Declaration of Mode During a Demonstration
Many times, we declare mode variables during demonstrations. We will again enter a skeleton of a demonstration; for example, in the demonstration of P ⊆ Q:
P c= Q
let x be set;
assume x in P;
thus x in Q;
At this point, it is stated as let x be set;.
be mode name
With the above, we can declare mode during a demonstration. Of course, we can also state reserve x for set before hand.