Abstract syntactical tree. Other names: Kantorovich's tree, Abstract Syntax Tree (AST). An abstract syntactical tree is the final, marked, oriented tree the inner tops of which are correlated with the programming language's operands, and the leaves with the corresponding operands. Thus, the leaves are empty operators and serve only as variables and constants. AST differs from the parse tree in that it keeps only the essential information about the program while the parse tree, on the contrary, contains much unnecessary information. In this sense the abstract syntactical tree is a condensed form of the parse tree convenient for presenting the language constructions' structure from the semantics' viewpoint.