The input is scanned and replaced with the production rule from left to right in the ____ derivation.

The input is scanned and replaced with the production rule from left to right in the leftmost derivation.

In the context of formal grammar and syntax, a leftmost derivation is a process used to generate strings from a language grammar. In this approach, at each step, the leftmost non-terminal symbol in the currently derived string is replaced with one of its production rules. This method ensures that the derivation follows a systematic procedure, maintaining consistency with the order of operations specified by the grammar.

The leftmost derivation is particularly relevant in parsing algorithms, where it plays a crucial role in understanding how strings can be constructed from grammar rules. This contrasts with rightmost derivation, where the rightmost non-terminal is replaced in the sequence. Overall, leftmost derivation aids in the analysis of syntax trees and the construction of parse trees, which are essential in compiler design and programming language processing.