Logging to /Users/s/tmp/pari-07.04
GPRC Done.

        GP/PARI CALCULATOR Version 2.12.1 (development 25142-46eb34041)
          i386 running darwin (x86-64/GMP-6.2.0 kernel) 64-bit version
     compiled: Mar 22 2020, Apple clang version 11.0.0 (clang-1100.0.33.17)
                            threading engine: single
                 (readline v8.0 enabled, extended help enabled)

                     Copyright (C) 2000-2020 The PARI Group

PARI/GP is free software, covered by the GNU General Public License, and comes 
WITHOUT ANY WARRANTY WHATSOEVER.

Type ? for help, \q to quit.
Type ?17 for how to get moral (and possibly technical) support.

parisize = 40000000, primelimit = 1000000
(16:09) gp > "bravo"+"lei"
  ***   at top-level: "bravo"+"lei"
  ***                        ^------
  *** _+_: forbidden addition t_STR + t_STR.
  ***   Break loop: type 'break' to go back to GP prompt
break> break

(16:09) gp > concat("bravo","lei")
%1 = "bravolei"
(16:09) gp > T="bravo"
%2 = "bravo"
(16:10) gp > U="lei"
%3 = "lei"
(16:10) gp > S="jeito"
%4 = "jeito"
(16:10) gp > concat(T,U)
%5 = "bravolei"
(16:10) gp > TU=concat(T,U)
%6 = "bravolei"
(16:10) gp > US=concat(U,S)
%7 = "leijeito"
(16:10) gp > concat(T,US)
%8 = "bravoleijeito"
(16:10) gp > concat(TU,S)
%9 = "bravoleijeito"
(16:11) gp > concat(concat(T,U),S)
%10 = "bravoleijeito"
(16:11) gp > concat(T,concat(U,S))
%11 = "bravoleijeito"
(16:11) gp > concat(concat(T,U),S)==concat(T,concat(U,S))
%12 = 1
(16:11) gp > vazia=""
%13 = ""
(16:16) gp > concat(vazia,S)
%14 = "jeito"
(16:16) gp > concat(vazia,S)==S
%15 = 1
(16:16) gp > concat(S,vazia)
%16 = "jeito"
(16:16) gp > concat(S,vazia)==S
%17 = 1
(16:16) gp > concat(vazia,vazia)
%18 = ""
(16:16) gp > concat(vazia,vazia)==vazia
%19 = 1
(16:16) gp > znorder(Mod(2,15))
%20 = 4