Given R^n, R^m and R^l let D1⊂R^n and D2⊂R^m. Let f be a mapping of D1 into R^m?

and g be a mapping of D2 into R^l and assume f(D1) ⊂D2. Show that if f is a continuous at p_0 in D1 and g is continuous at f(p_0) in D2 then the composite mapping g o f is continuous at p_0