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Terminal symbols are the elementary symbols of the language defined as part of a formal grammar. Nonterminal symbols (or syntactic variables) are replaced by groups of terminal symbols according to the production rules. The terminals and nonterminals of a particular grammar are in two completely separate sets.
Here, the nonterminal T can generate all strings with more a's than b's, the nonterminal U generates all strings with more b's than a's and the nonterminal V generates all strings with an equal number of a's and b's. Omitting the third alternative in the rules for T and U does not restrict the grammar's language.
Unlike a semi-Thue system, which is wholly defined by these rules, a grammar further distinguishes between two kinds of symbols: nonterminal and terminal symbols; each left-hand side must contain at least one nonterminal symbol. It also distinguishes a special nonterminal symbol, called the start symbol.
A context-sensitive grammar is a noncontracting grammar in which all rules are of the form αAβ → αγβ, where A is a nonterminal, and γ is a nonempty string of nonterminal and/or terminal symbols. However, some authors use the term context-sensitive grammar to refer to noncontracting grammars in general. [1]
Terminal (macOS), a terminal emulator included with macOS; Windows Terminal, a terminal emulator for Windows 10 and Windows 11; GNOME Terminal, a Linux and BSD terminal emulator; Terminal and nonterminal symbols, lexical elements used in specifying the production rules constituting a formal grammar in computer science.
where A, B, and C are nonterminal symbols, the letter a is a terminal symbol (a symbol that represents a constant value), S is the start symbol, and ε denotes the empty string. Also, neither B nor C may be the start symbol, and the third production rule can only appear if ε is in L(G), the language produced by the context-free grammar G.
All the points illustrated by circles and diamonds are nodes in Figure 1, and the former are called nonterminal nodes and the latter terminal nodes. [2]
Let us notate a formal grammar as = (,,,), with a set of nonterminal symbols, a set of terminal symbols, a set of production rules, and the start symbol.. A string () directly yields, or directly derives to, a string (), denoted as , if v can be obtained from u by an application of some production rule in P, that is, if = and =, where () is a production rule, and , is the unaffected left and ...