%%HP: T(3)A(R)F(.);
\<< EXPAND
  IF { 28. 0. 1. }
OVER TYPE POS
  THEN ARG
  ELSE DUP RE SWAP IM
\-> X Y '2*ATAN(Y/(X+(\v/
((X^2)+(Y^2)))))'
EXPAND
    IF DUP \->LST {
ATAN } HEAD POS
    THEN DUP \->NUM \->Q\pi
EXPAND
      IF { \pi } \->ALG
DUP 2 \->LIST \|^MATCH
      THEN NIP
      ELSE DROP
      END
    END
  END
\>>