      A = { BEGIN END FUNCTION IF NOT STRING VAR WHILE } : 8
      B = { CONST FUNCTION IF INTEGER NOT STRING WHILE } : 7
    A+B = { BEGIN CONST END FUNCTION IF INTEGER NOT STRING VAR WHILE } : 10
    A-B = { BEGIN END VAR } : 3
    A*B = { FUNCTION IF NOT STRING WHILE } : 5
A xor B = { BEGIN CONST END INTEGER VAR } : 5
