An elementary inference requires almost no additional reasoning.

Example:

The Thirteenth Amendment abolished slavery.

Therefore slavery was no longer legally permitted under the constitutional order.

The relationship is extremely direct.

A complex inference requires several connecting propositions.

For example:

The Thirteenth Amendment abolished slavery

→ former slaves became legally free

→ they could enter employment contracts

→ employers could hire them without slave ownership

→ labor mobility increased

→ capitalist labor markets could expand.

The final conclusion is much farther from the initial fact.

The opposite of "elementary inference" is therefore not necessarily a special technical term. We can simply call it:

complex inference

multi-step inference

extended inference

I prefer multi-step inference because it tells the reader exactly what makes it complex.