Chen-Ruan Cohomology Rings Of T～6/Z₄ And T～6/(Z₂)～2

Chen and Ruan[CR1] defined a very interesting cohomology theory for orb-ifold, which is now called Chen-Ruan cohomology. Later Chen and Hu[CH] give adeRham model to compute the Chen-Ruan cohomology ring of abelian orbifold.The important feature in Chen and Hu's ideas is twist factor, through whichthe cohomology ring can be defined without going through holomorphic orbifoldcurves. According to their ideas, the primary objective of this paper is to computethe Chen-Ruan cohomology rings of T⁶/Z₄ and T⁶/(Z₂)².