Graphic Abstract
© Su Sana E. PStairs in perspective
© jorge scottCriss Cross
© Terry A. StoaZebra Stripes
© Donna La Mattino PagakisIreland Door Handle
© Linda D. LesterSquared Spiral Staircase
© Janice MezzacappaCity fish
© Lourdes M. MoraBridge, Newcastle UK
© Cathryn Gallacher