2⁢ⅈ⁢K⁢k⁢cn⁡(2⁢K⁢t,k)=∑n=-∞∞(-1)n⁢πsin⁡(π⁢(t-(n+12)⁢τ))=∑n=-∞∞(∑m=-∞∞(-1)m+nt-m-(n+12)⁢τ),