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© 2000-2017   Gérard P. Michon, Ph.D.

Style & Usage

By words, the mind is winged.
Aristophanes  (c. 448-384 BC) 


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SI Unit rules and style conventions  by  NIST.
Common Mathematical Symbols and Abbreviations  by  Isaiah Lankham.
Math in HTML (and CSS)  by  Jukka "Yucca" Korpela.
Intro C: Mini-FAQ on Words & Phrases
by  Mark Israel, Albert Marshall, Donna Richoux et al.
Hints, tips & help for writing mathematics well   (Purdue University, Calumet).
A Guide to Writing Mathematics by  Dr. Kevin P. Lee.
The NEW Friendly Numbers by  Pat Ballew  (Amicable vs. equal abundancy).

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The Longest Words in the English Language  by  Rocketboom.

Style and Usage Notes
English as the lingua franca of Science

(2005-06-11)   Scholarly Abbreviations
Remnants of an era when Latin was the language of knowledge.

Quid quid latine dictum sit, altum videtur.
Anything stated in Latin is perceived as profound.

No commas should follow any of the following Latin abbreviations, with only two exceptions  ("i.e." and "e.g.")  that  must  be followed by a comma.

Abbr.Read as (Latin)English translationUsage notes
c.circaaroundIndicates an approximate date.
et al.et aliiand othersEnds an incomplete list of people.
etc.et ceteraand so onEnds an incomplete list.
viz.viz.videlicetIntroduces a more explicit statement.
i.e.,id estthat isIntroduces an equivalent paraphrase.
e.g.,exempli gratiafor example
[avoid "example given"]
Introduces a specific example.
vs.versus[as] opposed toOpposition or contradistinction.
cf.conferrecompare toSuggests a comparative reference.
quod vide
quae vide
which seeA self-reference, for one item.
A self-reference, for several.
N.B.nota benenote wellIntroduces a delicate precision.
Q.E.D.quod erat
which was to
be proved
Marks the end of a proof.
(Halmos symbol is recommended.)
 ita estit is so...... like it or not.
Non-latin scholarly abbreviations are best confined to the language they originate from.  Examples include:
Abbr.LanguageMeaningUsage notes
Englishwithout loss
of generality
Introduces an arbitrary break of a
symmetry among parameters.

Medical abbreviations

Margaret Marks (2006-11-18)   Resp.
Is the abbreviation "resp." acceptable in a mathematical context?

Yes, but the word "respectively" and the symbol "resp." have different syntaxes.  The latter should probably be used exclusively in a mathematical context.  It's not  a general-purpose abbreviation of the former...

In her blog today (2006-11-18)  Margaret Marks  was kind enough to quote my two-line definition of signed infinities as an actual example of the mathematical use of "resp.".  (I just noticed this when someone triggered her link to <Numericana>.)

A (contrived) example would be:  "The square of 2 (resp. 3) is 4 (resp. 9)."

That could also be stated:  "The squares of 2 and 3 are 4 and 9 respectively."

The two syntaxes are different, as advertised.  Occasionally, the former syntax can be more convenient and mathematicians find it easier to  parse.

It's not a bad thing to have a few keywords which allow the reader to recognize an English sentence as a mathematical statement, because that may deeply affect the meaning...  The most critical feature is undoubtedly that mathematical discourse (expressed in any "natural language") is inclusive "by default"  whereas everyday speech is not.  To a mathematician, the statement "a circle is an oval" is clearly true.  It would seem nonsensical to people accustomed to a common  "exclusive"  definition stating, at the very outset, that an oval is a non-circular shape...

By comparison, the use of "resp." (which puzzled Margaret) is a minor issue !  However, this and other mildly jargonistic terms may actually be helpful in warning the reader that a sentence is meant to be a mathematical one  (which is to be interpreted as inclusively as possible, even if only "common" words are used).  Such clues help build what linguists call a "context".  Mathematical texts may acquire strange meanings when an attempt is made to read them "out of context".

Miguel Angel Urrutia (Panama, 2003-08-07)   Typography of Numbers
Why use  999998  when  999,998  seems more readable?

Separators are common in a financial context, but they are rarely used within scientific equations, where they would decrease readability rather than improve it.

Also, there are cultural differences for separators (dots or commas).  In English, the comma is used to separate 3-digit groups, whereas a period is used for the "decimal point".  In French it's the exact opposite.  A Frenchman who's otherwise fluent in English could easily misinterpret  999,998  to mean  999.998.

The 22nd CGPM  (October 2003) reaffirmed Resolution 7 of the 9th CGPM  (1948)  by ruling that  both  the comma and the dot were allowed as decimal markers.  Therefore,  neither  is acceptable in an international context as a typographical separator between groups of digits.  The international convention is to use some spacing between 3-digit slices.  If at all possible, such spacing should be thinner than the regular spacing between words.

Unless their rough magnitude is clear from the context, it's a good idea to avoid decimal numbers featuring exactly 3 digits after the decimal marker and 3 digits or less before it  (except in the unambiguous case of a single leading zero digit).  Many people could otherwise misinterpret such numbers by a factor of one thousand.

When separators are used, the need for an unsightly single-digit "group" is normally avoided by allowing the leading group to include up to 4 digits.  In particular, separators are not used for integers up to 9999.

Number theorists who deal routinely with large integers never use any separation between groups of digits (separators or spacing) because very large integers are unreadable  anyway.  In this digital age, a marginal improvement in readability is less important than the ability to  cut and paste  such long numbers uniformly.

Non-blank separators are never used to the right of the decimal marker.  Spacing between decimals is best restricted to the (rare) tabular display of  many decimals for a specific mathematical constant  (in which case groups of 5 or 10 decimals may be more typical than groups of 3).  The ISO 31-0 standard says:

" To facilitate the reading of numbers with many digits, these may be separated into suitable groups, preferably of three, counting from the decimal sign towards the left and the right.  The groups should be separated by a small space, and never by a comma or a point, nor by any other means. "

(2006-10-24)   Denoting Intervals
Use only square brackets; outward brackets for excluded extremities.

For example, [0,1] is the set of all real numbers between 0 and 1, both extremities included, whereas ]0,1] is the set of all nonzero such numbers.

We do not recommend a notation with ordinary parentheses for excluded extremities;  namely (0,1] in the latter example above.  It's unfortunately dominant in "domestic" English texts  (it puzzles international audiences).

The chief reason why the "domestic" notation is unacceptable is that  (0,1)  is universally accepted as denoting an ordered pair  (an element of a cartesian product)  in  any  modern context.  Using that same notation to denote  ]0,1[  is confusing at best, for  any  audience.

(2006-11-01)   International dates in numerical form
The above date is November 1st, 2006.

The year is listed first as a 4-digit number.  Dashes are used, not slashes.

Taken together, those two clues properly indicate that the date identification uses the international ISO 8601 standard in its  simplest  form...

That standard specifies that the most significant numbers must be listed first, as is the case with digits in ordinary decimal numeration  (thus, the month follows the year and the day of the month is listed in third position).  Months and days are always given as two-digit numbers, with a leading zero if necessary.  This design makes  lexical  and  chronological  orders coincide, as is most desirable.

This is simple and logical enough when it comes to identify a specific day.

Unfortunately, the standard also allows other formats for dates and times which cannot be assumed to be self-explanatory.  We think these are best ignored outside of specialized contexts  For example, separating dashes may be dropped, time can be included and a week number could be specified instead of a month number...  Such add-ons to the above basics only hinder general acceptance.

Compatible Customary Time Stamps

In digital contexts, ISO 8601 dates of the above type are sometimes followed by separate (nonstandard) time stamps.

Such customary time stamps feature a column character ":" between hours and minutes, from 00:00 to 23:59.  This is reminiscent of the ubiquitous displays for digital 24-hour clocks, which need  no introduction.  The only "unusual" part of the convention is a leading zero for the hours before 10am.

For added precision, another ":" may be added, followed by a two-digit number of seconds, from 00 to 59.  For the ultimate in precision, this number of seconds may be given with as many decimals as needed (using a decimal point).

Basic ISO 8601 dates followed by such time stamps  (with a single blank space inbetween)  identify a precise time.  By design, the lexicographical ordering of such identifications is the correct chronological order  (whether the time stamps are given at the same level of precision or not).  Examples:

2006-10-31 23:45
2006-11-01 04:05
2006-11-01 04:05:10
2006-11-01 04:05:10.3
2006-11-01 04:05:10.32346159
2006-11-01 04:06
2006-11-01 05:00

(D. L. of Manchester. 2000-12-07)
What are the names of the operands in common operations?

  • addend + addend = sum     (also:   term + term = sum)
  • minuend - subtrahend = difference
  • multiplier ´ multiplicand = product
    factor ´ factor = product   (mostly for  commutative  multiplications)
  • dividend / divisor = quotient
  • base exponent = power
  • indexÖradicand = root

With thanks to Steve Healey  ("BonusSpin")  of  Edison, NJ,  a  math & physics  junior at  Rutgers  (New Brunswick, NJ)  who appeared on the ABC TV show  "Who Wants to Be a Millionaire?"  on Sept. 14 & 17, 2000.

Thanks also to  Keith McClary  for suggesting (2004-05-24)  multiplier  and  multiplicand,  especially for  noncommutative  multiplications.

Note the consistent use of the suffixes, which are of Latin origin:
  • Dividend= "That which is to be divided" (the orator Cato ended all of its speeches with the famous quote "Carthago delenda est": Catharge is to be destroyed). In a nonmathematical context, dividends are profits that are to be divided among all shareholders.
  • Divisor = "That which is to do the dividing". A director does the directing, an advisor does the advising, etc. In ancient Rome, the Emperor was the "Imperator", the one supposed to issue the orders (Latin: "Imperare")

(2007-03-06)   Pronouncing Numbers
High-school parlance and straight talk.

In high-school parlance, the negative integer "-7" is pronounced "negative seven".  Outside of the classroom, almost everybody says: "minus 7".

The number 0.7 (namely seven tenth or 70% of a whole) is also written .7 and pronounced either "decimal seven" or "zero point seven" (the latter being preferred in modern "straight talk").

(2000-12-07)   Pronouncing Formulas
How do native speakers pronounce formulas in English.

Here are the basics:

  •  -x  :  "negative x"  or  "minus x".
  • x+y :  "x plus y".
  • x-y :  "x minus y".
  • x y :  "x times y" or "x into y"  (the latter is more idiomatic).
              (British English:  "x lots of y".)
  • x/y :  "x over y".   (British English:  "x on y".)
    • If x and y are both integers, y is pronounced as an ordinal: 3/4 = "three fourth".
    • When x is long to pronounce,  say it last using the locution: "all over y, x".   That's the equivalent of:  (1/y) x.
  • xy  : "x to the power of y".
    • Longer version (elementary level): "x raised to the power of y".
    • Shorter version (when x is easy to pronounce): "x to the y".
    • If y is an integer, "x to the yth [power]" ("power" is optional).
      Thus, "two to the four" and "two to the fourth" both mean  24.
    • If y is 2 or 3, "x square[d]" or "x cube[d]" are most common.
  • ê  :  e-roof or e-hat  (base vector, tensor, operator).
  • f o g  :  "f  after g "  or  "f  round g "  (e.g.,  composition of morphisms).

If  A  and  B  are strings,  I call their concatenation  "A before B".

There's also the issue of indicating parentheses and groupings when pronouncing expressions.  If the expression is simple enough, a parenthesis is adequately pronounced by marking a short pause.  For example,  x (y+z) / t  could be spoken out "x times ... y plus z ... over t" (pronouncing "y plus z" very quickly).

The locution "outside of" can also be used to introduce an opening parenthesis, matching a closing parenthesis corresponding to a short pause.

When dictating more complex expressions involving parentheses, it's best to say  open parent'  and  close parent'  as needed.

(2000-12-07)   PEMDAS?   Not.
The Meaning of it All.

From a semantical viewpoint, the  meaning  of complex arithmetical expressions involving elementary operators is the value obtained by applying the operators in their conventional order of precedence.  Unfortunately, English-speaking schoolchildren are often taught to associate this with the mnemonic sentence "Please Excuse My Dear Aunt Sally":  Parentheses first, then Exponentiations, Multiplications, Divisions, Additions and Subtractions... This should not be relied upon, for the following reasons:

  • It tells only part of the whole story.  The other essential part is that you must group things left to right when encountering operators of the same precedence.  For example:
    9-1-2-3 actually means (((9-1)-2)-3) = 3.
  • Addition and subtraction actually have the same precedence so that 9-3+2 is universally understood to mean (9-3)+2 = 8 (see previous point) and is not equated to the expression 9-(3+2) = 4, as it would be if addition had higher precedence than subtraction. 
  • With many computer languages (and/or scientific calculators), multiplication and division have the same precedence as well.  This means that 9/3´2 is actually worked out left to right to denote (9/3)´2 = 6 on many calculators, whereas the written expression may be intended to mean 9/(3´2) = 1½, according to the aforementioned  "PEMDAS"  rule (wrongly) taught to schoolkids.  When the latter is meant, it's probably better to use  9/3/2 

Use parentheses to make sure you're understood!

(2012-11-02)   Physical Units
Products and ratios of physical units.

The above issue arises for physical units, especially when an electronic  calculator  is involved.

For example,  the SI unit for  entropy  or  thermal capacity  is the  joule per kelvin  (J/K).  A specific thermal capacity is a thermal capacity per unit of mass, so the SI unit is the  joule per kelvin per kilogram  or  J/K/kg.  It's a bad idea to write that down as  J/K.kg  (joule per kelvin-kilogram)  because of the above ambiguity,  although most professionals won't even blink.  A modern trend  (which I dislike)  is to forgo the use of the division sign (the solidus)  entirely when expressing physical units.  According to this relatively new fashion, the abbreviation for the previous unit would be:

J . K-1 . kg-1   =   m2 . s-2 . K-1

I still favor  parsimony  and prefer to express gravitational fields in  N/kg  (newtons per kilogram)  rather than in   m/s/s ,    m/s2    or    m.s-2

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