HTML symbols

Need HTML help to write important things like :

Γ, A, A ⇒ Δ
--------------- (W)
Γ, A ⇒ Δ

or like :

Vr(λ) ↔ ¬Vr(λ)

on your blog/website ? Some people (myself included !) have found helpful to have a look there or drag the keyboard to the toolbar.