Source PostScript (arg.pps)

%% %% argument d'un complexe --> dans ]-180, 180]
%% /arg {
%%    exch atan
%%    dup 180 gt 
%% 	 {360 sub}
%%    if
%% } def

%% argument d'un complexe --> dans ]-180, 180]
/arg {
2 dict begin
   /y exch def
   /x exch def
   x 0 eq y 0 eq and {
       0
   } {
      y x atan
      dup 180 gt 
         {360 sub}
      if
   } ifelse
end
} def

%% 1 dict /argdict exch def
%% argdict /l@st@rg 0 def
%% argdict /l@st@rg get
%% prout

 /l@st@rg 0 def

/argc {
   exch atan
   dup 180 gt 
      {360 sub}
   if
   {
   dup l@st@rg sub -120 le
      {360 add}
      {exit}
   ifelse
   } loop
   {
   dup l@st@rg sub 120 ge
      {360 sub}
      {exit}
   ifelse
   } loop
   dup /l@st@rg exch store
} def