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Notations whose shape carries information nobody is told about. Brackets that turn an array into a single number; an arrow above a letter that says what type of object it is; half-serifs that encode which way a number rounds; an index above rather than below a symbol that flips how a quantity transforms; an equals sign that is not equality and depends on a modulus written at the end of the line. Every member of this family is a place where a reader who supplies the ordinary meaning gets a confidently wrong answer.
Square or round brackets enclosing a grid of numbers, marking a matrix.
Straight vertical bars around a square grid, denoting its determinant.
A short arrow written above a letter, marking it as a vector.
A capital O with a bracketed expression, bounding a growth rate from above.
Braces enclosing a variable, a separator and a condition, defining a set by a rule.
Square brackets with the top or bottom serifs removed, marking rounding direction.
Letters written above and below a symbol, marking a tensor's components.
Three stacked horizontal bars, marking congruence rather than equality.
A single wave-shaped stroke marking equivalence, similarity or distribution.
Mixed square and round brackets marking whether an endpoint is included.