2 isdefined - whether a string names a defined function
13 isdefined(str) returns 1 if str is the name of a builtin function,
14 2 if str is the name of a user-defined function, 0 otherwise.
41 isassoc, isatty, isblk, isconfig, iserror, iseven, isfile,
42 ishash, isident, isint, islist, ismat, ismult, isnull, isnum, isobj,
43 isobjtype, isodd, isprime, isrand, israndom, isreal, isrel,
44 issimple, issq, isstr, istype