1. The problem statement, all variables and given/known data Zwiebach's A First Course in String Theory Quick Calculation 2.5: Consider the plane (x,y) with the identification [tex](x,y)\rightarrow (x+2\pi R,y+2\pi R)[/tex]. What is the resulting space? 2. Relevant equations A one dimensional line with identification [tex]x\rightarrow x+2\pi R[/tex] is a circle. A plane with identifications [tex](x,y)\rightarrow (x+2\pi R,y)[/tex] [tex](x,y)\rightarrow (x,y+2\pi R)[/tex] is a torus. 3. The attempt at a solution The identification is just the combination of both of the torus identifications... but how would I join two boundaries with a single identification? And what would be the fundamental domain? Thanks!