Error(s), warning(s):

invalid bareword "0b19"
in expression "0b19 - 0b1";
should be "$0b19" or "{0b19}" or "0b19(...)" or ... (invalid binary number?)
    (parsing expression "0b19 - 0b1")
    invoked from within
"expr 0b$d - 0b1"
    (procedure "mul" line 5)
    invoked from within
"mul $a $b"
    invoked from within
"puts [mul $a $b]"
    (file "21592986/source.tcl" line 29)