Editing Tietze extension theorem (section)

==Equivalent statements==
This theorem is equivalent to [[Urysohn's lemma]] (which is also equivalent to the normality of the space) and is widely applicable, since all [[metric space]]s and all [[Compact space|compact]] [[Hausdorff space]]s are normal. It can be generalized by replacing <math>\R</math> with <math>\R^J</math> for some indexing set <math>J,</math> any retract of <math>\R^J,</math> or any normal [[Deformation retract#Retract|absolute retract]] whatsoever.