install_alias_method

# File lib/irb/extend-command.rb, line 155
    def install_alias_method(to, from, override = NO_OVERRIDE)
      to = to.id2name unless to.kind_of?(String)
      from = from.id2name unless from.kind_of?(String)

      if override == OVERRIDE_ALL or
          (override == OVERRIDE_PRIVATE_ONLY) && !respond_to?(to) or
          (override == NO_OVERRIDE) &&  !respond_to?(to, true)
        target = self
        (class << self; self; end).instance_eval{
          if target.respond_to?(to, true) &&
              !target.respond_to?(EXCB.irb_original_method_name(to), true)
            alias_method(EXCB.irb_original_method_name(to), to)
          end
          alias_method to, from
        }
      else
        print "irb: warn: can't alias #{to} from #{from}.\n"
      end
    end