if not
— Adverb
– English
~ perhaps; indicating possibility of being more remarkable (greater or better or sooner) than; "will yield 10% if not more"; "pretty if not actually beautiful"; "let's meet tonight if not sooner"
infix notation
— Noun
– English
~ a notation for forming mathematical expressions using parentheses and governed by rules of operator precedence; operators are dispersed among the operands
irrational number
— Noun
– English
~ a real number that cannot be expressed as a rational number
index number
— Noun
– English
~ a number or ratio (a value on a scale of measurement) derived from a series of observed facts; can reveal relative changes as a function of time
imaginary number
— Noun
– English
~ (mathematics) a number of the form a+bi where a and b are real numbers and i is the square root of -1