What Is Infix Operators?

Cited from Data Infix Operators in R

Infix refers to the placement of the arithmetic operator between variables. For example, an infix operation is given by (a+b), whereas prefix and postfix operators are given by (+ab) and (ab+), respectively.

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Cited from the Book "Beginning Data Science in R"

If you want help on an infix operator, you need to quote it, and you do that using backquotes.

?`+`