Urysohn and Tietze extensions of Lipschitz functions

Let (X,d) be a metric space and $\alpha > 0$. In this paper, we study extensions of some complex-valued Lipschitz functions, from some special subset $X_0$ to X. These extensions are with no-increasing Lipschitz number or the smallest Lipschitz number. Moreover, we show that under some conditions, Tietze extension theorem can be generalized for Lipschitz functions and call it Tietze-Lipschitz extension. Furthermore, we generalize Urysohn-lemma for Lipschitz functions. In fact we present a necessary and sufficient condition for that Lipschitz functions separate subsets of X.