By this I prove that sleep is not subtraction, but addition.
"Around The Tea-Table"
T. De Witt Talmage
In the possession of thirty, it needs a loss or gain of ten, in the possession of three hundred the addition or subtraction of a hundred, to bring us the same emotional excitement.
"Psychology and Social Sanity"
Hugo Münsterberg
Addition, subtraction, Multiplication, and Division.
"A Practical Enquiry into the Philosophy of Education"
James Gall