# Definition:Formal Grammar/Top-Down

(Redirected from Definition:Top-Down Grammar)

## Definition

Let $\mathcal L$ be a formal language whose alphabet is $\mathcal A$.

A top-down grammar for $\mathcal L$ is a formal grammar which allows well-formed formulas to be built from a single metasymbol.

Such a grammar can be made explicit by declaring that:

From the words thus generated, those not containing any metasymbols are the well-formed formulas.