The Three Functions of the English-Letter Indicator (RULE IV)

Preliminary Remarks

The English-letter indicator of the Nemeth code has three separate functions. It is easier to explain and state the rules for the use of this indicator by using different names for the indicator when it is used for the different functions. This page thus differentiates among the use of (dots 56) (1) as a letter sign for abbreviations, (2) as an English-letter indicator with special type forms, and (3) as a "Letter Indicator" required to distinguish mathematical symbols from contracted words. While this distinction is not always made explicit in standard Nemeth references, it seems to me to offer considerable simplification.

The name Letter Indicator is used here to simplify understanding the Nemeth rules and is not a standard term in Nemeth literature.


The braille cell dots 5-6, which is represented in Braille ASCII by the ASCII code corresponding to the semi-colon keyboard character, encompasses three semantic cells which all have the general meaning of "letter sign" in technical material transcribed according to the Nemeth Code. (This same cell has other uses including the indication of subscripts and certain final-letter contractions; these other uses are not addressed here.)

The three related semantic cells are:

Letter sign used with abbreviations in technical material because of rules similar to those in literary braille
English-Letter Alphabetic Indicator always used before an English letter used in a mathematical symbol when it is preceded by a type-form indicator (See also TNI.)
Nemeth Letter Indicator used when necessary to distinguish letters and letter sequences being used as symbols from the same strings being used as whole-word contractions. The LI is primarily needed in non-mathematical contexts, i.e., prose whereas the LS and ELI are used in all contexts. (A better name than letter indicator might be symbol indicator. The name comes from the use in indicating that a letter is a "just a letter" rather than a short-form word.)

Nemeth mathematical identifiers.

It is helpful to clarify some terms before explaining the use of the LI. In Nemeth the word symbol often means simply the braille cells used to transcribe a particular print item, generally called a print sign. This is not the way the word symbol is intended in this context.

MathML defines a mathematical identifier or mi as an element that "represents a symbolic name or arbitrary text that should be rendered as an identifier. Identifiers can include variables, function names, and symbolic constants." Words (whether spelled-out or contracted), acronyms, abbreviations, and the isolated endings used to form plurals, possessives, or ordinals are not mathematical identifiers.

This definition is a bit too general for Nemeth since the pre-defined function names of Rule XVII are given special treatment. Also the allowed characters are the literals and numerals; other cells including the letter signs of literary braille are not permitted. Nemeth does not apparently preclude the first character of a symbolic name from being a numeral but this restriction is almost always adhered to in technical material and will be assumed here.

Also with respect to "rendering", Nemeth does not indicate the italics commonly used to typeset mathematical items if these have no special significance.

A Nemeth mathematical identifer or Nmi is thus defined as a mathematical identifier subject to the following restrictions. The only characters allowed in an Nmi are the 26 literals and 10 numerals. An Nmi together with a plural, possessive, or ordinal ending is also an Nmi. The Rule XVII pre-defined function names, whether spelled out or abbreviated, are not Nmi's although other symbolic function names, such as the f in f(x) are Nmi's. An Nmi does not have to use any non-regular typeform used in print if the typeform has no particular mathematical significance.

Any Nmi is always a mathematical item that creates mathematical context whether or not it is preceded by an ELI or LI. This is an important rule: being in mathematical context affects the application of various other rules, including those for the use of the Punctuation Indicator and the form of the comma following an NMi. (See also Note 1.)

Roman numerals

Roman numerals are treated slightly differently in literary braille and in Nemeth.

Roman numerals with only one letter or "digit" in either upper- or lower-case and all multi-letter lower-case Roman numerals follow the rules for numbers, analogous to those for words, in that the default scope of a type-form indicator is the entire Roman numeral. However, the English-letter Indicator, rather than the Numeric Indicator, is used following the type-form indicator. See the use of the TNI for details.

A single-letter Roman numeral in either upper- or a lower-case and set in regular type and a multi-letter Roman numeral in all lower-case with at least the first letter set in regular type will require an LI in the same contexts as certain mathematical symbols. (This is different from literary braille in that an upper-case single-letter Roman numeral does not require a letter sign.)

A multi-letter Roman numeral that is all upper-case is treated as a word and not a mathematical symbol and is transcribed as in literary braille: immediately preceded by the double or word capitalization sign. Such Roman numerals when set in special type use the Type-Form Indicators for words and not the English-letter Indicator.

It is not correct syntax for a Roman numeral to be written in mixed case.

The literary letter sign or LS.

The name letter sign (LS) is used here to refer to the English-letter indicator when used with abbreviations according to the Nemeth rules which are similar to those of literary braille.

Most of the rules for using the letter sign with abbreviations that could be mistaken for short-form words are retained; this comprises all single-letter abbreviations plus lower-case letter sequences that correspond to short-form words.

If such an abbreviation is followed by a period which belongs to it or arguably belongs to it as well as being a period at the end of a sentence, then a letter sign is not used. However, such an abbreviation with no following period or no following period that can reasonably be considered as belonging to it requires a preceding LS. In some cases the same sequence of cells would be used for an abbreviation with no period as for a symbol using the same letter or letter sequence. This distinction will be indicated in properly marked-up text; otherwise, the meaning is usually obvious from context but could be a problem in back-translation.

More details about abbreviations can be found in Rule VIII of the Nemeth code. See Note 2 below for more about mixed-case and upper-case letter sequences.

The English-Letter Indicator or ELI.

The English-letter Indicator is required when an NMi has been individually set in non-regular type using one of the Rule V Type-Form Indicators for Letters. The ELI is not used when an NMi is set in non-regular type as a result of being in a phrase or mathematical expression that is set in non-regular type using Type-Form Indicators for Phrases and Mathematical Statements. See also Rule V, Sec. 33. (See related rules for the use of the TNI.)

The Nemeth Alphabetic Indicators [Rule IV] are used to indicate that the following letter is from a particular alphabet. The scope of all of the Alphabetic Indicators is only one letter. A letter affected by an Alphabetic Indicator, even the English-Letter Indicator, must be a mathematical symbol (NMi), not a single-letter contraction or part of a word. (See Rule V for words set in non-regular type.) Since the English alphabet is the default, there are situations where an ELI is not required even though another Alphabetic Indicator would be.

Any individual English letter in an NMi can be marked up with none or more of the indicators in the following order (p. 208):

The Type-form Indicator is optional but if a Type-form Indicator is used, a following Alphabetic Indicator is always required in all contexts, even for English (Roman) letters. According to rule 34b, default mathematical italics often used in print are not indicated in braille since their function is accomplished by use of the Letter Indicator described in the next section and other aspects of Nemeth.

Note that the Alphabetic Indicator is required for all alphabets except the English alphabet and is only used for the English alphabet when preceded by the Type-Form Indicator. (However, this rule should not be interpreted to apply to cell dots 56 in its role as an LI.) An Alphabetic Indicator always precedes any Capitalization Indicator.

The Capitalization Indicator is optional but when used is always placed immediately before the letter.

Click here for examples of the use of the ELI.

Remember that these rules for the use of the ELI apply to letters used in mathematical symbols. Type-form indicators are used as in literary braille for text set in non-regular type subject to Nemeth formatting rules.

The use of special type-forms with Roman numerals was described earlier.

Nemeth Letter Indicator 25-28.

[This summary does not incorporate the special rules for use of the Letter Indicator in Tables and Diagrams that are addressed in 29 and 30.)

The LI is different from the LS, the ELI and also the Numeric and Punctuation Indicators in that both the preceding and following contexts must be considered in order to determine its proper use.

Special Nemeth mathematical identifiers

The purpose of the LI is to avoid confusion between Nmi's and certain whole-word contractions which are here called Special Nemeth mathematical identifiers. The LI plays somewhat the same role as do mathematical "italics" or other special rendering as would be produced by a LATeX $x$ in print. The additional complexity has two causes:

A Special Nemeth mathematical identifier or SNmi is an NMi that happens to use the same letter or sequence of letters that can also be used as a word (a, I, or O), a single-letter contraction for a word, or a short-form contraction for a word in literary braille. An SNmi is thus either one of the 26 letters of the alphabet or one of the 49 letter sequences listed in the following Table. [Literal cells in symbols are sometimes referred to in Nemeth literature as "letters in their own right".]

Possible "short-form letter combinations"
ab ac af agal bl cd ei fr gdhm ll
lr pdqksd tdtm tnwd xf xs yr
abvacrafnafw almalraltalw brldcldcv
grthmf imm myfnec neircvrjc tgryrf
dclgdcvgrcvgrjcg yrvs

The Table is comprised of all the Grade 2 Braille short-form word contractions that don't use part-word contractions or an embedded apostrophe [25-b-i].

What is required for an SNmi or Roman numeral to be eligible for an LI?

An LI is only used with an eligible SNmi or an eligible Roman numeral.

An LI is never used with an Nmi that is not an SNmi.

An SNmi or Roman numeral—with or without a plural, possessive, or ordinal ending—is eligible if it is unembellished with subscripts, superscripts, or any modifiers and all of its letters are letters from the English (Roman) alphabet and none of its letters requires a preceding ELI as a result of being set in special type. (See also Note 3 and Note 4.) Also, if it consists of more than one letter all of the letters must be lower-case. (See also Note 2.)

An elgible SNmi of one letter is called a "single letter" when it is in a context where an LI must precede it. [Rule IV, Sec. 25.]

An elgible SNmi of more than one letter is called a "short-form letter combination" or "short-form combination" when it is in a context where an LI must precede it. [Rule IV, Sec. 25.]

The scope of an LI, in contrast to that of an ELI, is the entire symbol even if it consists of more than one letter. (There can be no conflict with the use of an ELI since an LI is never used with an NMi or Roman numeral with one or more characters individual set in special type.)

It is not correct to use an LI "just in case".

Which contexts require an LI with an eligible symbol?

A Letter Indicator is only used before eligible SNmi's or eligible Roman numerals embedded in contexts where one might possibly mistake them for words, i.e. literary or non-mathematical contexts. In order for an LI to be required, the eligible SNmi or eligible Roman numeral must be both preceded and followed by literary context.

Contexts where an LI is used with eligible SNmi's and Roman numerals

An LI is not used with any SNmi or Roman numeral that is the content of a "simple label" or an item in an enclosed list. Taking into account these two exceptions—where an SNMi or Roman numeral can be in contact with an unembellished grouping symbol without the need for an LI—an LI is used with those eligible SNmi's and Roman numerals that

are delimited by being preceded [25-a-v] by either a literary space, linebreak, or any punctuation mark and also by being followed [25-a-vi] by either a literary space, linebreak, or any punctuation mark or would be so preceded if not for an intervening unembellished Rule XVIII grouping symbol [28a] or would be so followed if not for an intervening unembellished Rule XVIII grouping symbol.

Click here for examples of the use of the LI. Click here for examples of the use of the LI in the case of grouping symbols.

COMMENTS. Rules 25-a-v and 25-a-vi refer to punctuation marks in ink print.

A comma following any mathematical item, including a symbol, must be transcribed by one of the mathematical commas in order to eliminate the need for a punctuation indicator. That a symbol in an otherwise literary context must be followed by the dot 6 comma rather than the standard one or by a Punctuation Indicator is not sufficient reason for not using an LI. (A contracted comma can only be used in a mathematical context.)

A hyphen or short dash either preceding or following a symbol is literary context with respect to the symbol. [Rule IV 26b] An eligible SNmi in contact with a hyphen or short dash always requires an LI.

Special consideration is given to the grouping symbols because, even though they are mathematical symbols, they can appear in literary context either followed or preceded by words or abbreviations.

Contexts where an LI is never used

The rules for where an LI is used are also sufficient to determine where an LI is not used; this section is added for clarity. The non-use of the LI for SNmi's in contact with mathematical contexts is complemented by Rule VIII which forbids the use of contractions and short-form words in such contexts.

  1. The LI is not used with symbols in a mathematical expression even when they are the first item in the expression since the following context is mathematical.
  2. The LI is not used with an embellished SNMi[25-a-iii] even if it is not otherwise part of a mathematical expression because either or both the preceding or following context would be mathematical. [A symbol is said to be embellished if it has any subscript, superscript, prime or modifier.]
  3. The LI is not used in a simple label, that is with any symbol that is in direct with both its opening and closing grouping signs if both grouping signs are unembellished, e.g., (a) or [iii].
  4. The LI is not used with an otherwise eligible SNMi that is an item in an enclosed list [27-d].
  5. The LI is not used with an element of a matrix or determinant [27-c].
  6. It is incorrect to use an LI in any other context not explicitly mentioned in these rules.

Miscellaneous Notes

Note 1. Punctuation following a symbol.

Any Nmi together with an optional plural, possessive, or ordinal ending creates math context. Because the the context is math, math punctuation, such as a mathematical comma, must be used whenever possible following the symbol in order to avoid the need for a Punctuation Indicator; otherwise, a Punctuation Indicator is needed prior to transcribing punctuation immediately following the symbol. Also, the math context is, of course, maintained if the symbol is followed by non-context-changing punctuation such as a hyphen or an unembellished grouping symbol so any subsequent literary punctuation requires a Punctuation Indicator.

Note 2. Mixed-case and upper-case letter sequences.

The reason that none of the letters in a multi-letter NSmi can be upper-case [25-b-ii] is that a mixed-case letter sequence is always assumed to be an NSmi and is also distinguished by the use of a single capital-letter indicator before each upper-case letter. A symbol that uses all upper-case letters is distinguished from an acronym by the use of a single capital-letter indicator before each letter; an acronym, like a word, is preceded by the double capital-letter sign.

Note 3. Symbols set in special type

The reason that an NMi does not require the use of an LI if any of its letters uses a non-English alphabet or individually uses a special type form such as bold-face is simply because the required Alphabetic Indicator(s) are sufficient to distinguish the letter(s) as a symbol. When (dots 56) are required before a letter from the English alphabet because of the use of a special type form the cell is known as the English-letter Indicator and not what is called here the Letter Indicator.

Note 4. Symbols within passages set in special type

If a SNmi is set in special type as a result of being in a passage set in special type, then it is not automatically exempt from eligibility for an LI.

Note 5. Embellished Symbols

Superscripts, subscripts, and modifiers are mathematical items in Nemeth. If a symbol were to be embellished it could not be both preceded by and followed by literary context. .

Note 5. Common Errors.
According to the National Library Service (NLS) the most common Nemeth errors involving the English-letter Indicator are as follows:
  1. Using an LI with a symbol preceding or following a sign of comparison (LI's are not used in mathematical expressions)
  2. Forgetting to use an LI with a symbol mentioned in a sentence
  3. Unfamiliarity with the term variable as a "letter substituted for unknown numbers"

Last updated February 21, 2002.

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