#import std #import nat #comment -[ toy example of a self-describing algebraic expression represented by a tree of type %sfOZXT]- nterm = ('+',sum=>0)^: < ('*',product=>1)^: <('3',3!)^: <>,('4',4!)^: <>>, ('-',difference+~&hthPX)^: <('9',9!)^: <>,('2',2!)^: <>>>
