satisfy the assumptions of Theorem
3.3 and Moreover the following conditions hold:
(a) f and T commute weakly.
(b) x ∈ F ix(f) implies x ∈ fT(x).
Then T and f have a common fixed point in M.
Proof. By the proof of Theorem 3.3, there exits x0 ∈ M such that x0 ∈
fT(x0). Using condition (a) and (b), we obtain
x0 = f(x0) ∈ fT(x0) ⊆ T f(x0) = T(x0).
Thus, x0 must be a common fixed point of f and T