Mechanism

The causal route: what actually does the work that produces your result. Swap the engine, not the packaging. Two candidates that run on the same engine are one candidate, no matter how different they look on the surface.

The causal route: what actually does the work that produces your result. Swap the engine, not the packaging. Two candidates that run on the same engine are one candidate, no matter how different they look on the surface.

Example

For Spanish, solo drilling is one engine. A weekly video tutor runs a different one: live pressure and correction from another person. Switching apps keeps the engine, so a second and third app count as one option, not three.