[ $ \
try:
    float(string_from_stack())
except:
    to_stack(False)
else:
    to_stack(True)
 \ python ]                                     is isfloat (   $ -->   b )

 [ nextword
   dup isfloat not if
     [ $ '"f" needs to be followed by a number.'
       message put bail ]
   ' [ ' ] swap nested join
   nested swap dip join ]                   builds f       ( [ $ --> [ $ )

  [ $ \
import math
a = string_from_stack()
a = str(math.sin(float(a)))
string_to_stack(a) \ python ]                   is sin     (   $ -->   $ )

  [ $ \
import math
a = string_from_stack()
a = str(math.asin(float(a)))
string_to_stack(a) \ python ]                   is asin    (   $ -->   $ )

  [ $ \
import math
a = string_from_stack()
a = str(math.cos(float(a)))
string_to_stack(a) \ python ]                   is cos     (   $ -->   $ )

  [ $ \
import math
a = string_from_stack()
a = str(math.acos(float(a)))
string_to_stack(a) \ python ]                   is acos    (   $ -->   $ )

  [ $ \
a = string_from_stack()
b = string_from_stack()
c = str(float(b) * float(a))
string_to_stack(c) \ python ]                   is f*      ( $ $ -->   $ )

  [ $ \
a = string_from_stack()
b = string_from_stack()
c = str(float(b) / float(a))
string_to_stack(c) \ python ]                   is f/      ( $ $ --> $   )

  [ $ \
a = string_from_stack()
b = string_from_stack()
c = str(float(b) ** float(a))
string_to_stack(c) \ python ]                   is f**     ( $ $ --> $   )