Substitution

The substitution of E for all free occurrences of v in E2 is written E2[E/v].

v[E/v] = E

x[E/v] = x when x not= v

c[E/v] = c

(E1 E2)[E/v] = (E1[E/v])(E2[E/v])

(v.E1)[E/v] = (v.E1)

(x.E1)[E/v] = x.(E1[E/v]) when x not=v and x not in fv(E)

and = y.((E1[y/x])[E/v]) when x not=v and x is in fv(E) and y not in fv(E1 E).