Let f be a function defined on an open interval containing c (except possibly at c) and let L be a real number. Then: lim f(x) = L (as x-->c) means that for each Epsilon>0 there exists a Delta>0 such that if 0<[x - c]<Delta, then [f(x) - L]<Epsilon.

If f is continuous on the closed interval [a,b] and k is any number between f(a) and f(b), then there is at least one number c in [a,b] such that f(c) = k

If h(x) <_f(x) <_ g(x) for all x in an open interval containing c, except possibly at c itself, and if lim(as x-->c) h(x) = L = lim(as x-->c) g(x) then lim(as x -->c) f(x) exists and is equal to L.