發送短信 : Graphs with three eigenvalues and second largest eigenvalue at most 1

 _    _      ___     _    _      ___       _____  
| \  / ||   / _ \\  | || | ||   / _ \\    / ___// 
|  \/  ||  | / \ || | || | ||  | / \ ||   \___ \\ 
| .  . ||  | \_/ || | \\_/ ||  | \_/ ||   /    // 
|_|\/|_||   \___//   \____//    \___//   /____//  
`-`  `-`    `---`     `---`     `---`   `-----`