def subst( hash )
      self.class.new @dest.subst( hash ), @weight.subst( hash ),
                     *@sources.collect { |source| source.subst hash }
    end
def subst( hash )
      self.class.new @dest.subst( hash ), @weight.subst( hash ),
                     *@sources.collect { |source| source.subst hash }
    end
Substitute variables

 Substitute the variables with the values given in the hash.

 @param [Hash] hash Substitutions to apply.

 @return [Node] Term with substitutions applied.

 @private