→ Notation used in the following

ast_ref_tree(?Language:atom, ?ArgumentName:atom)

• In the meta-model of language arg1, arg2 is the name of AST node arguments that represent references (that is identities of other nodes that are neither children nor parents which can be referenced with ast_sub_tree). For instance, in the Java AST arguments named ref are references.:

    ast_ref_tree('Java', ref).

• In particular, the ref argument used above in the definition of callT, is a reference to the invoked method.