Erdal Karapinar, Ph.D., is a Professor in the Department of Mathematics at Cankaya University and Visiting Professor at the China Medical University of Taichung. He completed his Ph.D. at the Middle East Technical University (METU), Turkiye. He is the co-author of one book, more than 10 chapters for edited books, and more than 400 research articles in peer-reviewed journals. His research interests include functional analysis and metric fixed point theory.Ravi P. Agarwal, Ph.D., is a Professor in the Department of Mathematics at the Texas A&M University-Kingsville. He completed his Ph.D. at the Indian Institute of Technology, Madras, India, in 1973. Dr. Agarwal has authored or co-authored 50 books and 1,750 research articles. His research interests include nonlinear analysis, differential and difference equations, fixed point theory, and general inequalities.

• Metric Spaces.- Extension of Metric Spaces.- Fixed Point Theorems on Extended Metric Spaces.