Chapter 6. Tacticals

An interactive definition is started by giving a definition command omitting the definiens. An interactive proof is started by using one of the proof commands omitting an explicit proof term.

An interactive proof or definition can and must be terminated by a qed command when no more sequents are left to prove. Between the command that starts the interactive session and the qed command the user must provide a procedural proof script made of tactics structured by means of tacticals.

In the tradition of the LCF system, tacticals can be considered higher order tactics. Their syntax is structured and they are executed atomically. On the contrary, in Matita the syntax of several tacticals is destructured into a sequence of tokens and tactics in such a way that is is possible to stop execution after every single token or tactic. The original semantics is preserved: the execution of the whole sequence yields the result expected by the original LCF-like tactical.