rpn
reverse polish · stack-based · zero parens · undo with U
sin
cos
tan
ln
log
√
^
1/x
±
n!
7
8
9
÷
drop
4
5
6
×
swap
1
2
3
−
dup
0
.
π
+
↵ enter
tap U to undo · keys: 0-9 + - * / ^ enter (space) backspace · functions = first letter
← z5