Learn Spanish (Latin America): De haber anticipado su apertura, habría evitado el jaque mate. - If I had anticipated his opening, I would have avoided the checkmate.

Using de followed by an infinitive is a common way to create a conditional "if" clause in Spanish. Because this is a hypothetical about the past, it uses the perfect infinitive haber anticipado (to have anticipated). It means the exact same thing as the past subjunctive Si hubiera anticipado but is a slightly more advanced, concise structure.

How do we know the subject is "I" when there is no pronoun?

The phrase De haber anticipado uses an infinitive, which doesn't show the person. The main verb habría evitado is in the conditional perfect, which shares the same form for the first person (I) and third person (he/she/you formal). Without extra context, it is ambiguous. The translation assumes "I" based on a typical scenario where a chess player is analyzing their own game, but it could just as easily mean "If he had anticipated... he would have avoided..."

Is apertura a specific chess term for "opening"?

Yes. Just like in English, apertura translates literally to "opening" (such as the opening of a new store or event), and it is also the exact technical term used for the established first few moves in a game of chess.

What are the origins of the phrase jaque mate?

Jaque mate is a masculine compound noun, which is why it uses el. In Spanish chess terminology, jaque means "check" and mate means "mate". It is almost always written as two separate words, though they act as a single noun phrase.