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How to write math on a typewriter

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Here is a topic that remains relevant even today with all our advancements in computer-aided typesetting: How to write math on a typewriter. Though we have TeX and MathML, neither of these have become standard enough that they can be used on the Web with the confidence that they will be understood by anyone using any browser. Adding to the confusion, some people treat CAS (like Maple or Mathematica) syntax as if it were proper mathematical notation.

Thus, some of the old conventions from typewritten math articles remain relevant in math discussion forums as well as in OEIS sequence entries.

Operation Typewriter Typeset
Assignment k = 1
k := 1
The use of ":=" comes from computer programming languages.
Equality testing or asserting a = b
a == b
The use of "==" comes from computer programming languages.
Inequality testing or asserting a ≠ b
a != b
Type "=" then backspace once and type "/", or viceversa. This option is of course unavailable to some math discussion forums, which then avail themselves to "!=" from computer programming languages.
Less than a < b
Less than or equal a ≤ b
a =< b
a <= b
Type "<" then backspace once and type "_", or viceversa. The problem with "<=" is that it looks like an arrow.
Greater than a > b
Greater than or equal a ≥ b
a >= b
a => b
Type ">" then backspace once and type "_", or viceversa. The problem with "=>" is that it looks like an arrow.
Addition a + b
Subtraction a - b In a fixed-width font, the difference between an en dash and an em dash (- and –) is irrelevant.
Multiplication 2 * pi * r
Exponentiation 2^p
Fractions 1/(x - y) Note that parenthesis become crucial to avoid a misinterpretation of operator precedence.
(p^q - 1)/(p - 1)
Sum sum ((-1)^k)/(3k + 2)) {k = 0 .. inf}
Sum ((-1)^k)/(3k + 2)) : 0 <= k<= inf)
Other iterated operations like products and integrals also show a variety of notation for the iteration.
Product
Limits
Binomial coefficients C(n, k)
Legendre symbol (a/p) The problem here isn't distinguishing among these three related but different symbols, but distinguishing them from fractions. Hence it would be much clearer to write legendre(a, p) or equivalent as needed.
Jacobi symbol
Kronecker symbol
Pochhamer symbol (x)n There is so much confusion about the notation of Pochhammer symbol it might be better to eschew the shortcut in favor of writing out a product or factorial.

See also