Jack

A Jack is an action statement. Each Jack expresses one meaningful action in a consistent form, making it sufficient to be understood on its own. Jacks are the atomic building block of a Jack Tree.

A Jack always follows a verb + noun form (e.g. “Validate customer address,” “Calculate shipping cost”) — never a noun alone, a question, or a compound statement joining two actions.

When a Jack Tree node is decomposed into child Jacks, it should normally produce two or more of them. A node that decomposes into only one child is a signal to check the tree: either a sibling Jack is missing, or the node didn’t need decomposing at all.

The one-action constraint keeps each Jack independently testable and traceable — a requirement for the TRACE structure a Jack Tree builds toward. A compound Jack (two actions joined into one statement) breaks that: it can’t be individually verified, and it hides which part of it a downstream Injector or Semaphore attribute is actually about.

The “two or more” rule guards against false decomposition. A node with a single child usually means one of two things: the child is really just a restatement of the parent (no new information added — remove the extra level), or a sibling Jack genuinely exists but hasn’t been surfaced yet (go back to Jack Points and look again). Since Stackable means meaning comes from a Jack’s position in the hierarchy rather than from extra wording, an unjustified single-child level distorts that meaning for everything beneath it.