bf quick reference vocabulary
-----------------------------
!  exclamation mark - ( d v -) store d into v
:  colon - ( v - d ) fetch variable content
@  at - ( [f] - x*d ) execute function [f]
?  question mark - ( f [f] | [f1] [f2] - x*d ) if-then or if-then-else
   execute [f] if f or execute [f1] if f, otherwise [f2]
#  number - ( [f1] [f2] - x*d ) while [f1] execute [f2]
t  stop parsing until end of input line
%  percent - ( n - n n ) dup
;  semi-colon - ( n - ) drop
$  dollar - ( n1 n2 - n2 n1 ) swap
_  underscore - ( n3 n2 n1 - n2 n1 n3 ) rot
r  ( x*d n - y*d ) roll, rotate nth element
p  ( x*d n1 - x*d n2 ) pick, copy n1th element
:  colon - show stack content
)  right parenthesis - ( x*d - ) empty stack
}  right curly bracket - ( - n ) leave current stack depth
*  asterisk - ( n1 n2 - n1*n2 ) multiplication
+  plus - ( n1 n2 - n1+n2 ) addition
-  hyphen - ( n1 n2 - n1-n2 ) subtraction
/  slash - ( n1 n2 - n1/n2 ) integer division
m  ( n1 n2 - n3 ) - modulo (integer remainder)
^  circumflex accent - ( n1 n2 - n3 ) n2th power of n1
!  exclamation mark - ( n1 n2 - n3 ) n2th root of n1
\  backslash - ( n - -n ) negate TOS
g  ( n1 - n2 | ) generate n2, a random number from 0 to n1 if n1 is not 0,
   or set seed if n1 = 0
=  equal - ( d1 d2 - f ) True if d1 = d2
>  greater than - ( d1 d2 - f ) True if d1 > d2
&  ampersand - ( n1 n2 - f ) logical and
|  vertical bar - ( n1 n2 - f ) logical or
l  letter el - ( n1 n2 - f ) logical xor
~  tilde - ( n - f ) logical not
a  ( n1 n2 - n3 ) bitwise and
o  ( n1 n2 - n3 ) bitwise or
n  ( n1 - n2 ) bitwise not (1s complement)
x  ( n1 2n - n3 ) bitwise xor
i  ( n - ) print TOS on standard output
j  ( n1 n2 - ) print n1 in a field of n2 chars on standard output
k  ( n1 n2 - ) print n1 with n2 decimal digits on standard output
]  right square bracket - ( - ) toggle appending input lines to buffer file
y  ( "s" - ) yield stack content to file "s"
<  lesser than - ( - "s" ) read input from standard input
(  left parenthesis - ( "s" - x*d ) read and execute input from file
`  grave - ( - n ) leave on TOS ascii code of next char
'  single quote - ( n - ) emit char whose ascii code is on TOS
,  comma - ( "s" - n ) convert string on TOS to number
.  period - emit a Carriage Return
e  ( "s1" n1 - "s2" | n2 ) extract as string "s2" n1th char of "s1" if
   n1 is zero or positive, or its length n2 if n1 is negative
u  ( "s" - n | "s1" "s2" 0 - "s1+s2" | "s1" n1 n2 - "s2" )
   unveil first ascii code of a string, unify strings or get substrings
h  help on system commands
d  list current directory
c  ( "s" - ) change directory
v  print vocabulary by screens
z  toggle debugging zone
q  ( n - ) quit with error code n
b  ( "s" - ) set buffer file name to "s"
f  ( - "s" ) leave current buffer file name in "s"
s  ( "s" - ) show content of file "s"
w  print working directory
