@ ProgramNode (location: (1,0)-(3,11))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(3,11))
    └── body: (length: 2)
        ├── @ AliasGlobalVariableNode (location: (1,0)-(1,11))
        │   ├── new_name:
        │   │   @ GlobalVariableReadNode (location: (1,6)-(1,8))
        │   │   └── name: :$a
        │   ├── old_name:
        │   │   @ BackReferenceReadNode (location: (1,9)-(1,11))
        │   │   └── name: :$+
        │   └── keyword_loc: (1,0)-(1,5) = "alias"
        └── @ AliasGlobalVariableNode (location: (3,0)-(3,11))
            ├── new_name:
            │   @ GlobalVariableReadNode (location: (3,6)-(3,8))
            │   └── name: :$a
            ├── old_name:
            │   @ GlobalVariableReadNode (location: (3,9)-(3,11))
            │   └── name: :$b
            └── keyword_loc: (3,0)-(3,5) = "alias"