HP 48gII Advanced User's Reference Manual page 120

Consider this example:
ACOS
Arc Cosine Analytic Function: Returns the value of the angle having the given cosine.
This diagram indicates that the analytic function ACOS (Arc Cosine) takes a single argument from level 1 and returns
one result (to level 1). ACOS can take either a real or complex number or an algebraic object as its argument. In the
first case, it returns the numeric arccosine; in the second, it returns the symbolic arccosine expression of the
argument.
Some commands affect a calculator state — a mode, a reserved variable, a flag, or a display — without taking any
arguments from the stack or returning any results to the stack. No stack diagrams are shown for these commands.
Parallel Processing with Lists
This feature is discussed in greater detail in Appendix G.
As a rule-of-thumb, a command can use parallel list processing if all the following are true:
The command checks for valid argument types. Commands that apply to all object types, such as DUP, SWAP,
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ROT, and so forth, do not use parallel list processing.
The command takes exactly one, two, three, four, or five arguments, none of which may itself be a list.
!
Commands, such as "LIST, that have an indefinite number of arguments do not use parallel list processing.
The command is not a programming branch command (IF, FOR, CASE, NEXT, and so forth).
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There are also a few commands (PURGE, DELKEYS, SF and FS? are examples) that have list processing capability
built into their definitions, and so do not also use the parallel list processing feature.
How Commands Are Alphabetized
Commands appear in alphabetical order. Command names that contain special (non-alphabetic) characters are
organized as follows:
For commands that contain both special and alphabetic characters:
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A special character at the start of a command name is ignored. Therefore, the command %CH follows the
"
command CF and precedes the command CHOOSE.
A special character within or at the end of a command name is considered to follow "Z" at the end of the
"
alphabet. Therefore, the command R"B follows the command RSWP and precedes the command R"C. The
only exception would be the "Σ" character which, when not the first character in the name, is alphabetized as if
it were the string "SIGMA". An example is "NΣ", which falls between NOVAL and NSUB.
Commands that contain only special characters appear at the end of the dictionary.
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Classification of Operations
The command dictionary contains hp48gII/hp49g+ commands, functions, and analytic functions. Commands are
calculator operations that can be executed from a program. Functions are commands that can be included in
algebraic objects. Analytic functions are functions for which hp48gII/hp49g+ provides an inverse and a derivative.
The definitions of the abbreviations used for argument and result objects are contained in the following table,
"Terms Used in Stack Diagrams." Often, descriptive subscripts are added to convey more information.
3-2 Full Command and Function Reference
"
Level 1
"
z
"
'symb'
Level 1
arc cos z
'ACOS(symb)'