use the Leibniz notation δx and δy for changes or increments in the variables x and y
use the notation δx/δy for the difference quotient [f(x+h)−f(x)]/h where y=f(x)
use the Leibniz notation for the derivative: dy/dx=lim_δx→0 δy/δx and the correspondence dy/dx=f′(x) where y=f(x)
