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# Demiclosedness principle and approximation theorems for certain classes of multivalued mappings in Hilbert spaces

- Felicia O Isiogugu
^{1}Email author

**2013**:61

https://doi.org/10.1186/1687-1812-2013-61

© Isiogugu; licensee Springer 2013

**Received:**19 July 2012**Accepted:**24 February 2013**Published:**18 March 2013

## Abstract

We prove weak and strong convergence theorems and the demiclosedness property for classes of multivalued mappings *T* such that ${P}_{T}$ is not nonexpansive, where ${P}_{T}x=\{u\in Tx:\parallel x-u\parallel =d(x,Tx)\}$. Thus our results extend and improve the results on multivalued and single-valued mappings in the contemporary literature.

**MSC:**47H10, 54H25.

## Keywords

- proximinal sets
- Hilbert spaces
- nonexpansive-type mappings
*k*-strictly pseudocontractive-type mappings- pseudocontractive-type mappings

## 1 Introduction

*E*be a normed space. A subset

*K*of

*E*is called proximinal if for each $x\in E$ there exists $k\in K$ such that

*K*is a closed and convex subset of a uniformly convex Banach space

*X*, then for any $x\in X$ there exists a unique point ${u}_{x}\in K$ such that (see,

*e.g.*, [1, 2])

*X*by $P(X)$, the family of all nonempty closed, convex and bounded subsets of

*X*by $CVB(X)$, the family of all nonempty closed and bounded subsets of

*X*by $CB(X)$ and the family of all nonempty subsets of

*X*by ${2}^{X}$ for a nonempty set

*X*. Let $CB(E)$ be the family of all nonempty closed and bounded subsets of a normed space

*E*. Let

*H*be the Hausdorff metric induced by the metric

*d*on

*E*, that is, for every $A,B\in {2}^{E}$,

*E*be a normed space. Let $T:D(T)\subseteq E\to {2}^{E}$ be a multivalued mapping on

*E*. A point $x\in D(T)$ is called a

*fixed point*of

*T*if $x\in Tx$. The set $F(T)=\{x\in D(T):x\in Tx\}$ is called a fixed point set of

*T*. A point $x\in D(T)$ is called a

*strict fixed point*of

*T*if $Tx=\{x\}$. The set ${F}_{s}(T)=\{x\in D(T):Tx=\{x\}\}$ is called a strict fixed point set of

*T*. A multivalued mapping $T:D(T)\subseteq E\to {2}^{E}$ is called

*L*-

*Lipschitzian*if there exists $L>0$ such that, for any pair $x,y\in D(T)$,

*T*is said to be a

*contraction*, while

*T*is

*nonexpansive*if $L=1$.

*T*is called

*quasi-nonexpansive*if $F(T)=\{x\in D(T):x\in Tx\}\ne \mathrm{\varnothing}$ and, for all $p\in F(T)$,

Clearly, every nonexpansive mapping with nonempty fixed point set is quasi-nonexpansive.

In recent years, several works have been done on the approximation of fixed points of multivalued nonexpansive mappings by many authors (see, for example, [3–5] and references therein). Different iterative schemes have been introduced by several authors to approximate the fixed points of nonexpansive mappings (see, for example, [3–5]). Among the iterative schemes, Sastry and Babu [3] introduced Mann and Ishikawa iteration as follows.

*p*be a fixed point of

*T*. The sequence of Mann iterates is given for ${x}_{0}\in X$ by

where ${y}_{n}\in T{x}_{n}$ is such that $\parallel {y}_{n}-p\parallel =d(T{x}_{n},p)$ and ${\alpha}_{n}$ is a real sequence in $(0,1)$ ${\sum}_{n=1}^{\mathrm{\infty}}{\alpha}_{n}=\mathrm{\infty}$.

where ${z}_{n}\in T{x}_{n}$, ${u}_{n}\in T{y}_{n}$ are such $\parallel {z}_{n}-p\parallel =d(p,T{x}_{n})$, $\parallel {u}_{n}-p\parallel =d(T{y}_{n},p)$ and $\{{\alpha}_{n}\}$, $\{{\beta}_{n}\}$ are real sequences satisfying: (i) $0\le {\alpha}_{n},{\beta}_{n}<1$; (ii) ${lim}_{n\to \mathrm{\infty}}{\beta}_{n}=0$; (iii) ${\sum}_{n=1}^{\mathrm{\infty}}{\alpha}_{n}\beta =\mathrm{\infty}$.

Using the above iterative schemes, Panyanak [4] generalized the result proved by [3].

Nadler [6] made the following useful remark.

**Lemma 1**

*Let*$A,B\in CB(X)$

*and*$a\in A$.

*If*$\gamma >0$,

*then there exists*$b\in B$

*such that*

Using Lemma 1, Song and Wang [5] modified the iteration process due to Panyanak [4] and improved the results therein. They made the important observation that generating the Mann and Ishikawa sequences in [3] is in some sense dependent on the knowledge of the fixed point. They gave their iteration scheme as follows.

*K*be a nonempty convex subset of

*X*, let ${\alpha}_{n},{\beta}_{n}\in [0,1]$ and ${\gamma}_{n}\in (0,\mathrm{\infty})$ such that ${lim}_{n\to \mathrm{\infty}}{\gamma}_{n}=0$. Choose ${x}_{1}\in K$, ${z}_{1}\in T{x}_{1}$. Let

where ${z}_{n}\in T{x}_{n}$, ${u}_{n}\in T{y}_{n}$ satisfy $\parallel {z}_{n}-{u}_{n}\parallel \le H(T{x}_{n},T{y}_{n})+{\gamma}_{n}$, $\parallel {z}_{n+1}-{u}_{n}\parallel \le H(T{x}_{n+1},T{y}_{n})+{\gamma}_{n}$ and $\{{\alpha}_{n}\}$, $\{{\beta}_{n}\}$ are real sequences in $[0,1)$ satisfying ${lim}_{n\to \mathrm{\infty}}{\beta}_{n}=0$, ${\sum}_{n=1}^{\mathrm{\infty}}{\alpha}_{n}{\beta}_{n}=\mathrm{\infty}$.

Using the above iteration, they then proved the following theorem.

**Theorem 1** (Theorem 1, [5])

*Let* *K* *be a nonempty compact convex subset of a uniformly convex Banach space* *X*. *Suppose that* $T:K\to CB(K)$ *is a multivalued nonexpansive mapping such that* $F(T)\ne \mathrm{\varnothing}$ *and* $T(p)=\{p\}$ *for all* $p\in F(T)$. *Then the Ishikawa sequence defined as above converges strongly to a fixed point of* *T*.

*X*is a normed space and $T:D(T)\subseteq E\to P(X)$ is any multivalued mapping, then the mapping ${P}_{T}:D(T)\to P(X)$ defined for each

*x*by

has the property that ${P}_{T}(q)=\{q\}$ for all $q\in F(T)$. Using this idea, they removed the strong condition ‘$T(p)=\{p\}$ for all $p\in F(T)$’ introduced by Song and Wang [5].

*et al.*[9] as follows:

where ${v}_{n}\in {P}_{T}({x}_{n})$, ${u}_{n}\in {P}_{T}({y}_{n})$ and $\lambda \in [0,1)$. Also, using a lemma in Schu [10], the idea of removal of the condition ‘$T(p)=\{p\}$ for all $p\in F(T)$’ introduced by Shahzad and Zegeye [7] and the method of direct construction of a Cauchy sequence as indicated by Song and Cho [11], they stated the following theorems.

**Theorem 2** (Theorem 1, [8])

*Let* *X* *be a uniformly convex Banach space satisfying Opial’s condition and* *K* *be a nonempty closed convex subset of* *X*. *Let* $T:K\to P(K)$ *be a multivalued mapping such that* $F(T)\ne \mathrm{\varnothing}$ *and* ${P}_{T}$ *is a nonexpansive mapping*. *Let* $\{{x}_{n}\}$ *be the sequence as defined in* (7). *Let* $(I-{P}_{T})$ *be demiclosed with respect to zero*. *Then* $\{{x}_{n}\}$ *converges weakly to a point of* $F(T)$.

However, we observe that there are many multivalued mappings *T* for which neither *T* nor ${P}_{T}$ is nonexpansive. Based on the above observation, it is our purpose in this paper to firstly introduce the new classes of multivalued nonexpansive-type, *k*-strictly pseudocontractive-type and pseudocontractive-type mappings which are more general than the class of multivalued nonexpansive mappings. Secondly, we prove that if *H* is a real Hilbert space and *K* is a nonempty weakly closed subset of *H*, $T:K\subseteq H\to P(H)$ is a multivalued mapping from *K* into the family of all nonempty proximinal subsets of *H*. Suppose that ${P}_{T}$ is a *k*-strictly pseudocontractive-type mapping. Then $(I-{P}_{T})$ is demiclosed at *zero* (*i.e.*, the graph of $I-{P}_{T}$ is closed at *zero* in $\sigma (E,{E}^{\ast})\times (E,\parallel \cdot \parallel )$ or weakly demiclosed at *zero*), where *I* denotes the identity on *E*, $\sigma (E,{E}^{\ast})$ the weak topology, $(E,\parallel \cdot \parallel )$ the norm (or strong) topology and ${P}_{T}x=\{u\in Tx:\parallel x-u\parallel =d(x,Tx)\}$. Lastly, we prove weak and strong convergence theorems for these classes of multivalued mappings without the compactness condition on the domain of the mappings using Mann and Ishikawa iteration schemes. Thus our results extend and improve the results on single-valued and multivalued mappings in the contemporary literature.

In the sequel, we will need the following definitions and lemmas.

**Definition 1** (See, *e.g.*, [12])

Let *E* be a Banach space. Let $T:D(T)\subseteq E\to {2}^{E}$ be a multivalued mapping. $I-T$ is said to be *strongly demiclosed* at *zero* if for any sequence ${\{{x}_{n}\}}_{n=1}^{\mathrm{\infty}}\subseteq D(T)$ such that ${x}_{n}$ converges strongly to *p* and a sequence $\{{y}_{n}\}$ with ${y}_{n}\in T{x}_{n}$ for all $n\in \mathbb{N}$ such that $\{{x}_{n}-{y}_{n}\}$ converges strongly to *zero*, then $p\in Tp$ (*i.e.*, $F(T)\ne \mathrm{\varnothing}$).

Observe that if *T* is a multivalued Lipschitzian mapping, then $I-T$ is strongly demiclosed.

**Definition 2** (See, *e.g.*, [12, 13])

Let *E* be a Banach space. Let $T:D(T)\subseteq E\to {2}^{E}$ be a multivalued mapping. $I-T$ is said to be *weakly demiclosed* at *zero* if for any sequence ${\{{x}_{n}\}}_{n=1}^{\mathrm{\infty}}\subseteq D(T)$ such that $\{{x}_{n}\}$ converges weakly to *p* and a sequence $\{{y}_{n}\}$ with ${y}_{n}\in T{x}_{n}$ for all $n\in \mathbb{N}$ such that $\{{x}_{n}-{y}_{n}\}$ converges strongly to *zero*, then $p\in Tp$ (*i.e.*, $0\in (I-T)p$).

**Definition 3** Let *E* be a Banach space. Let $T:D(T)\subseteq E\to {2}^{E}$ be a multivalued mapping. A point $p\in E$ is called an *asymptotic fixed point of* *T* if there exists a sequence ${\{{x}_{n}\}}_{n=1}^{\mathrm{\infty}}\subseteq D(T)$ such that $\{{x}_{n}\}$ converges weakly to *p* and a sequence $\{{y}_{n}\}$ with ${y}_{n}\in T{x}_{n}$ for all $n\in \mathbb{N}$ such that $\{{x}_{n}-{y}_{n}\}$ converges strongly to *zero*. We denote the set of asymptotic fixed points of *T* by $\stackrel{\u02c6}{F}(T)$.

**Definition 4** (See, *e.g.*, [12, 13])

Let *E* be a Banach space. Let $T:D(T)\subseteq E\to {2}^{E}$ be a multivalued mapping. The graph of $I-T$ is said to be *closed* in $\sigma (E,{E}^{\ast})\times (E,\parallel \cdot \parallel )$ (*i.e.*, $I-T$ is *weakly demiclosed* or *demiclosed*) if for any sequence ${\{{x}_{n}\}}_{n=1}^{\mathrm{\infty}}\subseteq D(T)$ such that $\{{x}_{n}\}$ converges weakly to *p* and a sequence $\{{y}_{n}\}$ with ${y}_{n}\in T{x}_{n}$ for all $n\in \mathbb{N}$ such that $\{{x}_{n}-{y}_{n}\}$ converges strongly to *y*, then $y\in (I-T)p$ (*i.e.*, $y=p-v$ for some $v\in Tp$).

**Definition 5** ([14])

*H*be a real Hilbert space. Let $T:H\to CB(H)$ be a multivalued mapping.

*T*is said to be monotone if given $x,y\in H$ and $u\in Tx$, there exists $v\in Ty$ such that

**Definition 6** ([5])

**Definition 7**Let

*E*be a real Banach space. Let $T:E\to {2}^{E}$ be a multivalued mapping. $I-T$ is said to be monotone in the sense of [14] if given any pair $x,y\in E$ and $u\in Tx$, there exists $v\in Ty$ such that

**Lemma 2** ([15])

*Let*$\{{a}_{n}\}$, $\{{\beta}_{n}\}$

*and*$\{{\gamma}_{n}\}$

*be sequences of nonnegative real numbers satisfying the following relation*:

*where* ${n}_{0}$ *is a nonnegative integer*. *If* $\sum {\beta}_{n}<\mathrm{\infty}$, $\sum {\gamma}_{n}<\mathrm{\infty}$, *then* ${lim}_{n\to \mathrm{\infty}}{a}_{n}$ *exists*.

**Lemma 3** ([11])

*Let*

*K*

*be a normed space*.

*Let*$T:K\to P(K)$

*be a multivalued mapping and*${P}_{T}(x)=\{y\in Tx:\parallel x-y\parallel =d(x,Tx)\}$.

*Then the following are equivalent*:

- (1)
$x\in Tx$;

- (2)
${P}_{T}x=\{x\}$;

- (3)
$x\in F({P}_{T})$.

*Moreover*, $F(T)=F({P}_{T})$.

**Lemma 4**

*Let*

*H*

*be a real Hilbert space*.

*Then the following well*-

*known result holds*:

*if*${\{{x}_{n}\}}_{n=1}^{\mathrm{\infty}}$

*is a sequence in*

*H*

*which converges weakly to*$z\in H$,

*then*

## 2 Main results

**Definition 8**Let

*X*be a normed space. A multivalued mapping $T:D(T)\subseteq X\to {2}^{X}$ is said to be

*k*-

*strictly pseudocontractive-type*in the sense of Browder and Petryshyn [16] if there exists $k\in [0,1)$ such that given any $x,y\in D(T)$ and $u\in Tx$, there exists $v\in Ty$ satisfying $\parallel u-v\parallel \le H(Tx,Ty)$ and

If $k=1$ in (9), *T* is said to be a *pseudocontractive-type* mapping. *T* is called nonexpansive-type if $k=0$. Clearly, every multivalued nonexpansive mapping is a nonexpansive-type mapping.

From the definitions, it is clear that every multivalued nonexpansive-type mapping is *k*-strictly pseudocontractive-type and every *k*-strictly pseudocontractive-type mapping is pseudocontractive-type. The following examples show that the class of nonexpansive-type mappings is properly contained in the class of *k*-strictly pseudocontractive-type mappings and the class of *k*-strictly pseudocontractive-type mappings is properly contained in the class of pseudocontractive-type mappings.

**Example 1**Let $X=\mathbb{R}$ (the reals with usual metric). Define $T:[0,\mathrm{\infty})\to {2}^{\mathbb{R}}$ by

Consequently, *T* is *k*-strictly pseudocontractive-type with $k=\frac{7}{12}$. It then follows that *T* is pseudocontractive-type. Observe that *T* is not nonexpansive-type so that the class of multivalued nonexpansive-type mappings is properly contained in the class of multivalued *k*-strictly pseudocontractive-type mappings. Next, we show that the class of multivalued pseudocontractive-type mappings properly contains the class of multivalued *k*-strictly pseudocontractive-type mappings.

**Example 2**Let $X=\mathbb{R}$ (the reals with usual metric). Define $T:[0,\mathrm{\infty})\to {2}^{\mathbb{R}}$ by

It then follows that *T* is a pseudocontractive-type mapping but not a *k*-strictly pseudocontractive-type mapping.

Using the multivalued version of the method of the proof used in [17], we then prove the following.

**Proposition 1** *Let* *E* *be a real Banach space*. *Suppose* $T:D(T)\subset E\to {2}^{E}$ *is a pseudocontractive*-*type mapping*. *Then* $I-T$ *is monotone*.

*Proof*Since

*T*is pseudocontractive-type, for any pair $x,y\in D(T)$ and $u\in Tx$, there exists $v\in Ty$ such that

Hence, $\u3008x-u-(y-v),x-y\u3009\ge 0$. Hence, $I-T$ is monotone. □

**Proposition 2** *Let* *E* *be a normed space*. *And let* $T:D(T)\subseteq E\to {2}^{E}$ *be a* *k*-*strictly pseudocontractive*-*type mapping*. *Then* *T* *is a* *L*-*Lipschitzian mapping*.

*Proof*Let

*T*be a

*k*-strictly pseudocontractive-type mapping. Then there exists $k\in [0,1)$ such that, for all $x,y\in D(T)$ and $u\in Tx$, there exists $v\in Ty$ satisfying $\parallel u-v\parallel \le H(Tx,Ty)$ and

□

**Proposition 3** *Let* *H* *be a real Hilbert space*. *Let* *K* *be a nonempty weakly closed subset of H*. *Let* $T:K\subseteq H\to P(H)$ *be a multivalued mapping from* *K* *into the family of all nonempty proximinal subsets of* *H*. *Suppose that* ${P}_{T}$ *is a* *k*-*strictly pseudocontractive*-*type mapping*. *Then* $(I-{P}_{T})$ *is demiclosed at zero* (*i*.*e*., *the graph of* $I-{P}_{T}$ *is closed at zero in* $\sigma (E,{E}^{\ast})\times (E,\parallel \cdot \parallel )$ *or weakly demiclosed at zero*).

*Proof*Let ${\{{x}_{n}\}}_{n=1}^{\mathrm{\infty}}\subseteq K$ be such that $\{{x}_{n}\}$ converges weakly to

*p*and a sequence $\{{y}_{n}\}$ with ${y}_{n}\in {P}_{T}{x}_{n}$ for all $n\in \mathbb{N}$ such that $\{{x}_{n}-{y}_{n}\}$ converges strongly to 0. We prove that $0\in (I-{P}_{T})p$ (

*i.e.*, $p=v$ for some $v\in {P}_{T}p$). Since ${\{{x}_{n}\}}_{n=1}^{\mathrm{\infty}}$ converges weakly, it is bounded. Let $q\in {P}_{T}p$ be arbitrary. From the definition of

*k*-strictly pseudocontractive-type, for each $n\in \mathbb{N}$, there exists ${v}_{n}\in {P}_{T}{x}_{n}$ such that

Hence it follows from (14) and (15) that $(1-k){\parallel p-q\parallel}^{2}=0$. Therefore $p=q\in Tp$. □

**Theorem 3**

*Let*

*K*

*be a nonempty closed and convex subset of a real Hilbert space*

*H*.

*Suppose that*$T:K\to P(K)$

*is a*

*k*-

*strictly pseudocontractive*-

*type mapping from*

*K*

*into the family of all proximinal subsets of*

*K*

*with*$k\in (0,1)$

*such that*$F(T)\ne \mathrm{\varnothing}$

*and*$T(p)=\{p\}$

*for all*$p\in F(T)$.

*Suppose*(

*I*-

*T*)

*is weakly demiclosed at zero*.

*Then the Mann type sequence defined by*

*converges weakly to* $q\in F(T)$, *where* ${y}_{n}\in T{x}_{n}$ *with* $\parallel {x}_{n}-{y}_{n}\parallel =d({x}_{n},T{x}_{n})$ *and* ${\alpha}_{n}$ *is a real sequence in* $(0,1)$ *satisfying*: (i) ${\alpha}_{n}\to \alpha <1-k$; (ii) $\alpha >0$; (iii) ${\sum}_{n=1}^{\mathrm{\infty}}{\alpha}_{n}(1-{\alpha}_{n})=\mathrm{\infty}$.

*Proof*

Since $\alpha >0$, from (ii), we have that ${lim}_{n\to \mathrm{\infty}}\parallel {x}_{n}-{y}_{n}\parallel =0$. Also, since *K* is closed and $\{{x}_{n}\}\subseteq K$ with $\{{x}_{n}\}$ bounded, there exists a subsequence $\{{x}_{{n}_{t}}\}\subseteq \{{x}_{n}\}$ such that $\{{x}_{{n}_{t}}\}$ converges weakly to some $q\in K$. Also, ${lim}_{n\to \mathrm{\infty}}\parallel {x}_{n}-{y}_{n}\parallel =0$ implies that ${lim}_{n\to \mathrm{\infty}}\parallel {x}_{{n}_{t}}-{y}_{{n}_{t}}\parallel =0$. Since $(I-T)$ is weakly demiclosed at *zero*, we have that $q\in Tq$. Since *H* satisfies Opial’s condition [18], we have that $\{{x}_{n}\}$ converges weakly to $q\in F(T)$. □

**Corollary 1** *Let* *H* *be a real Hilbert space and* *K* *be a nonempty closed and convex subset of* *H*. *Let* $T:K\to P(K)$ *be a multivalued mapping from* *K* *into the family of all proximinal subsets of* *K* *with* $F(T)\ne \mathrm{\varnothing}$. *Suppose* ${P}_{T}$ *is a* *k*-*strictly pseudocontractive*-*type mapping with* $k\in (0,1)$. *Then the Mann sequence* $\{{x}_{n}\}$ *defined in Theorem * 3 *converges weakly to a point of* $F(T)$.

*Proof* The proof follows easily from Lemma 3, Proposition 3 and Theorem 3. □

**Remark 1** It is easy to see that Examples 1 and 2 satisfy the condition ‘given any pair $x,y\in D(T)$ and $u\in Tx$ with $\parallel x-u\parallel =d(x,Tx)$, there exists $v\in Ty$ with $\parallel y-v\parallel =d(y,Ty)$ satisfying the conditions of Definition 8’. Also, if *T* is a multivalued mapping such that ${P}_{T}$ is a pseudocontractive-type mapping, then given any pair $x,y\in D(T)$ and $u\in {P}_{T}x$ with the corresponding $v\in {P}_{T}y$ satisfying the conditions of Definition 8, it is the case that $\parallel x-u\parallel =d(x,{P}_{T}x)$ and $\parallel y-v\parallel =d(y,{P}_{T}y)$.

Based on Lemma 3 and Remark 1 above, we will first prove weak and strong convergence for the new class of pseudocontractive-type mappings with the following two conditions: (i) given any pair $x,y\in D(T)$ and $u\in Tx$ with $\parallel x-u\parallel =d(x,Tx)$, there exists $v\in Ty$ with $\parallel y-v\parallel =d(y,Ty)$ satisfying the conditions of Definition 8; (ii) $T(p)=\{p\}$ for all $p\in F(T)$, then obtain the case for an arbitrary multivalued mapping *T* such that ${P}_{T}$ is a pseudocontractive-type mapping without the two conditions on ${P}_{T}$ as corollary.

**Theorem 4**

*Let*

*K*

*be a nonempty closed and convex subset of a real Hilbert space*

*X*.

*Suppose that*$T:K\to P(K)$

*is an*

*L*-

*Lipschitzian pseudocontractive*-

*type mapping from*

*K*

*into the family of all proximinal subsets of*

*K*

*such that*$F(T)\ne \mathrm{\varnothing}$

*and*$T(p)=\{p\}$

*for all*$p\in F(T)$.

*Suppose*,

*for any pair*$x,y\in K$

*and*$u\in Tx$

*with*$\parallel x-u\parallel =d(x,Tx)$,

*there exists*$v\in Ty$

*with*$\parallel y-v\parallel =d(y,Ty)$

*satisfying the conditions of Definition*8.

*Suppose*

*T*

*satisfies condition*(1).

*Then the Ishikawa sequence defined by*

*converges strongly to* $p\in F(T)$, *where* ${u}_{n}\in T{x}_{n}$ *with* $\parallel {x}_{n}-{u}_{n}\parallel =d({x}_{n},T{x}_{n})$, ${w}_{n}\in T{y}_{n}$ *with* $\parallel {y}_{n}-{w}_{n}\parallel =d({y}_{n},T{y}_{n})$ *satisfying the conditions in Definition * 8 *and* $\{{\alpha}_{n}\}$ *and* $\{{\beta}_{n}\}$ *are real sequences satisfying*: (i) $0\le {\alpha}_{n}\le {\beta}_{n}<1$; (ii) ${lim\hspace{0.17em}inf}_{n\to \mathrm{\infty}}{\alpha}_{n}=\alpha >0$; (iii) ${sup}_{n\ge 1}{\beta}_{n}\le \beta \le \frac{1}{\sqrt{1+{L}^{2}}+1}$.

*Proof*

*T*satisfies condition (1), ${lim}_{n\to \mathrm{\infty}}d({x}_{n},F(T))=0$. Thus there exists a subsequence $\{{x}_{{n}_{k}}\}$ of $\{{x}_{n}\}$ such that $\parallel {x}_{{n}_{k}}-{p}_{k}\parallel \le \frac{1}{{2}^{k}}$ for some $\{{p}_{k}\}\subseteq F(T)$. From (21)

*K*is closed. Now,

Hence, $q\in Tq$ and $\{{x}_{{n}_{k}}\}$ converges strongly to *q*. Since $lim\parallel {x}_{n}-q\parallel $ exists, we have that ${x}_{n}$ converges strongly to $q\in F(T)$. □

**Corollary 2** *Let* *H* *be a real Hilbert space and* *K* *be a nonempty closed and convex subset of* *H*. *Let* $T:K\to P(K)$ *be a multivalued mapping from* *K* *into the family of all proximinal subsets of* *K* *such that* $F(T)\ne \mathrm{\varnothing}$. *Suppose* ${P}_{T}$ *is an* *L*-*Lipschitzian pseudocontractive*-*type mapping*. *If* *T* *satisfies condition* (1), *then the Ishikawa sequence* $\{{x}_{n}\}$ *defined in* (16) *converges strongly to* $p\in F(T)$.

*Proof* The proof follows easily from Lemma 3, Remark 1 and Theorem 4. □

## Declarations

### Acknowledgements

This work was carried out at the University of Kwazulu Natal, South Africa when the author visited under the OWSDW [formally TWOWS], Abdus Salam International Centre for Theoretical Physics (ICTP) Trieste, Italy, Postgraduate Training Fellowship. She is grateful to OWSDW for the Fellowship and to University of Kwazulu Natal for making their facilities available and for hospitality.

## Authors’ Affiliations

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